List of Characters in The Percy Jackson and The Olympians Series and In The Heroes of Olympus Series - Creatures and Monsters

Creatures and Monsters

• Agrius and Oreius - Agrius and Oreius are humanoid bears that were a result of a union between a woman and a bear due to the power of Aphrodite. The two served as Luke's henchmen in The Sea of Monsters.

• Antaeus - Antaeus is a half-giant who is the son of Poseidon and Gaia. He was invincible as long as he maintained contact with the ground, so Percy defeated him by hanging him in the air with chains.

• Argus - Argus is a humanoid figure with eyes all over his body who works as a security guard at Camp Half-Blood. He rarely speaks as he is said to have an eye on his tongue. He cares for Hera a lot because she is his mother.

• Arion - Arion is a horse born to Poseidon and Ceres. He appears in The Son of Neptune where Hazel frees him from the Amazons. He is described as having a tan coat with a black mane and tail. He is a free spirit and seems to have a bad temper, being known to cuss when his abilities are challenged.

• Aurae - The Aurae are wind spirits who work at Camp Jupiter as seen in The Son of Neptune.
  • Mellie - An Aurae. She is the personal assistant of Aeolus as seen in "The Lost Hero." At the end of The Lost Hero she works as Piper's dad's assistant, Tristan McLean.

• Automaton - Automatons are similar to highly developed robots, with intricate circuitry that makes them hard to fix. Most are made out of steel but some, like Festus the dragon, are made out of celestial bronze or other materials. In the Percy Jackson & the Olympians series, Annabeth discovers that many statues in Manhattan are actually automatons created by Daedalus, an army that could either defend or attack Olympus.
  • Argentium - Reyna's silver Automaton Hound who appears in The Son of Neptune and The Mark of Athena.
  • Aurum - Reyna's gold Automaton Hound who appears in The Son of Neptune and The Mark of Athena.

• Basilisk - Basilisks are small green snakes with colorful spikes and poisonous bites and they can breathe fire. In The Son of Neptune, they attacked Camp Jupiter, but Frank shapeshifts into a mongoose (or weasel) and scares them off.

• Bronze Dragon - An automaton dragon made of bronze created by the campers in Hephaestus' cabin to help defend Camp Half-Blood. He is first shown in "Percy Jackson and the Bronze Dragon" story of "The Demigod Files" where Percy, Annabeth, and Silena reactivate it in order to save Charles Beckendorf from the Myrmekes. He was deactivated by Beckendorf with Percy's help afterwards, due to the fact that it was unstable and dangerous. It is fixed by the Hephaestus cabin to protect the camp sometime after this. He is later named "Festus" by Leo Valdez in "The Lost Hero" when Leo found him hidden in the forest. Leo manages to forge some wings onto Festus. Although Festus was sliced to bits by the lasers on King Midas' mansion, Festus' head was recovered by Hephaestus who had his cabin build the Argo II with Festus' head as the ship's figurehead. Festus means "happy" in Latin.

• Cacus - Cacus is a fire-breathing giant. In The Demigod Diaries story titled "Percy Jackson and the Staff of Hermes," Cacus had stolen Hermes' Caduceus. He later attacked Percy Jackson and Annabeth Chase. Annabeth hit Cacus with her metal claw and Percy killed Cacus with Hermes' Caduceus.

• Centaur - Centaurs are half man, half horse creatures, often depicted as wild and drunk. Chiron is the only truly civilized centaur. Many of his kin are part of the Party Ponies. There are other centaurs who work for Gaea's army.
  • Party Ponies - They are Chiron's kin. As their name suggests, they are a vast clan-like extended family of rowdy centaurs who reside in the United States with chapters hailing from each respective state. They are key players in two major incidents in the series. In The Sea of Monsters, they go along with Chiron and rescue Percy from Luke during their duel on the Princess Andromeda. In The Last Olympian, they help Chiron and the others fight the major battle between the gods and the Titans.
    • Larry - Member of the Party Ponies.
    • Owen - Member of the Party Ponies.

• Cerberus - The three-headed dog who guards the entrance to the Underworld. In The Lightning Thief, he befriends Annabeth. He also appears in The Last Olympian when he is playing with Mrs. O'Leary. Cereberus is the son of Echidna and Typhon.

• Ceto - The most powerful sea monster in Greek Mythology and the brother of Phorcys. In The Mark of Athena, Keto appeared as a girl named Kate who is encountered in Phorcys' aquarium. When Gleeson Hodge discovered Phorcys' ruse, he freed Percy and Frank after knocking Kate out. After Percy, Gleeson, and Frank escape from the aquarium, Keto sent Skolopendra after them.

• Charybdis - One of the two monsters (the other being Scylla) who live on either side of a narrow channel of water. She takes the form of a giant mouth that swallows and releases water, creating whirlpools. she is described by Percy as an "orthodontist's nightmare".

• Chimera - A three-headed beast that is part lion, part goat, and has a snake-headed tail. It is first seen in the form of a Chihuahua. It confronted Percy atop the St. Louis Arch alongside its mother, Echidna. Overwhelmed by the creature and poisoned by its snake head, Percy was forced to jump into the water far below to escape it. It disappeared after Percy dove into the water.

• Clazmonian Sow - A flying pig that appeared directly after Hyperion was defeated. Percy defeats it with the help of Blackjack, a statue of Hermes, and the New York Public Library's two stone lion statues (that were really automatons).

• Cloud Nymph - Nymphs associated with the clouds.
  • Fleecy - A Cloud Nymph who appeared in The Son of Neptune where she works at R.O.F.L.

• Colchis Bull - Elephant-sized, fire-breathing bronze bulls created by Hephaestus, with horns of silver and of rubies. In The Sea of Monsters, some of these bulls attack Camp Half-Blood and are defeated by Tyson. They were later used to make the tracks for the Chariot Race.
• Cyclops - One eyed-giants who have three species as mentioned in The Lost Hero. The first are the elder cyclops, who are friendly and help the gods ever since the Titanomachy. Tyson is one of these. The second is the southern species who raise goats and live in caves. Polyphemus is one of these. The third is the northern group who helped the Titans make weapons. In The Last Olympian, some rogue Cyclopes were seen fighting with Kronos' army in "The Battle of Manhattan."
  • Ma Gasket - A female cyclops of the Northern Cyclops faction who is the mother of Sump and Torque. She appears in "The Lost Hero" when Jason, Piper, and Leo visit her factory. In "The Son of Neptune," Ma Gasket leads the Cyclopes in an attack on Camp Jupiter where she is defeated by Tyson.
  • Polyphemus - A cyclops of the Southern Faction. Percy Jackson and his friends encounter him on an island in "The Sea of Monsters." He is shown to be blind and there was also a reference about Odysseus being responsible for blinding him under the alias of "Nobody". He later tried to eat them.
  • Sump - The son of Ma Gasket who appears in "The Lost Hero".
  • Torque - The son of Ma Gasket who appears in "The Lost Hero."

• Draco Aionius - Some of these monsters attacked Camp Half-Blood while Percy Jackson was on his adventures in the Sea of Monsters.

• Drakon - A race of giant serpent-like creatures that are several millennia older than dragons. They come in two different types: Aethiopian and Lydian. In The Demigod Diaries story titled "Leo Valdez and the Quest for Buford," an unidentified Drakon appeared in the Camp Half-Blood Forest until it was ripped apart by the Maenads.
  • Aethiopian Drakon - One was being raised by Luke in The Sea of Monsters. When one of the Bear Twins seemed reluctant to do his bidding, Luke threatened to feed him to the Drakon. In The Battle of the Labyrinth, an Aethiopian Drakon was seen in the cargo bay of the Princess Andromeda.
  • Lydian Drakon - The oldest and fiercest of the Drakons. In The Last Olympian, Kronos unleashed it upon Manhattan where it killed many half-bloods before being killed by Clarisse La Rue.

• Dryad - Dryads are a species of nymphs that are associated with trees and forests.
  • Juniper - Juniper is a Dryad. She is Grover Underwood's girlfriend, and in "The Battle of the Labyrinth", she informs Percy that she has seen Luke Castellan using the entrance to the Labyrinth and that she has also seen Quintus/Daedalus using the entrance to the Labyrinth.

• Echidna - Part woman, part snake. She is the wife of Typhon and the mother of Cerberus, Chimera, Hydra, the Nemean Lion, and Ladon as well as several others not in the series. She is first seen as an old lady who owned a chihuahua which was actually Chimera in disguise. Echidna also detests that there is a marsupial that was named after her. She assisted Chimera in fighting Percy at the top of the St. Louis Arch. She and Chimera disappeared after Percy dove into the water.

• Eidolons - A race of spirits that can possess demigods. In The Mark of Athena, the Eidolons work for Gaea.

• Empousai - Seductive shape-shifting women who are similar in appearance to vampires but have one shaggy donkey leg and one bronze leg. Two Empusa pose as cheerleaders in "The Battle of the Labyrinth." In The Last Olympian, an unnamed Empousai appears as part of the truce party along with Prometheus, Morrain, and Ethan Nakumura. She stated that she was among the things that was released from Pandora's pithos.
  • Kelli - An Empousai that poses as a cheerleader in "The Battle of the Labyrinth." She was killed by Annabeth.
  • Tammi - An Empousai that poses as a cheerleader in "The Battle of the Labyrinth." She was killed by Percy Jackson.

• Erymanthian Boar - The Erymanthian Boar is a giant boar, a servant of Pan who appears in The Titan's Curse. Percy, Thalia, Zoë, Grover, and Bianca first encounter it in Cloudcroft, New Mexico where Grover realizes its potential as a form of rapid transportation.

• Faun - The fauns are Roman counterparts of satyrs. In contrast to Camp Half-Blood's helpful satyrs, the fauns are mostly beggars and are often used for amusement purposes.
  • Don - One of the Fauns that live at Camp Jupiter. In "The Son of Neptune," Percy and Hazel run into Don who needs money for making up bad lies. When Percy asks why the Fauns aren't like the Satyrs, Don states that Fauns are free-spirited.

• Feather-Shooting Bird - A type of large black bird that shoots its feathers like arrows. In "The Demigod Files," Phobos summons them to fight Clarisse after he steals Ares' war chariot.

• Fire-Breathing Horse - A race of horses bred at the Triple G Ranch for war purposes. Some are shown to pull Ares' war chariot.

• Flesh-Eating Horse - A group of female horses bred at the Triple G Ranch. Some of them tried to eat Percy while he was cleaning the stables.

• Flesh-Eating Sheep - A race of carnivorous sheep owned by Polyphemus. They help to guard the Golden Fleece. Described as being a big as a hippopotamus and attacking like piranhas.

• The Furies - The Furies are Hades' chief servants and torturers and they personally searched for Hades's Helm of Darkness, believing that Percy had stolen it.
  • Alecto - Alecto acted as Percy's pre-algebra teacher, Mrs. Dodds, in the first book. She is Hades's main servant and acted as the lawyer who rescued Nico and Bianca Di Angelo from the Lotus hotel.
  • Megaera - A Fury representing grudging.
  • Tisiphone - A Fury representing avenged murder.

• Gegeines - A race of six-armed giants in leather loincloths who appear in The Lost Hero. They are summoned by Enceladus to fight Jason, Piper, and Leo.

• Geryon - In this series, Geryon is described as having a normal head, a face weathered and brown from years in the sun, slick black hair, a pencil-thin moustache, two very beefy legs wearing a very large pair of Levis and 3 chests wearing a different colored shirt: green, yellow and red. In "The Battle of the Labyrinth," he is the owner of Triple G Ranch with Orthrus guarding the ranch. He gave Percy an apparently impossible task; cleaning out the stables of carnivorous horses (one the Labours of Hercules. Percy managed to completed the task, but Geryon went back on his deal to let Percy's friends free and the two fought. Percy found Geryon a strong opponent, as Geryon's three hearts made him almost impossible to defeat. Percy defeated Geryon with a well placed arrow (thanks to Hera) that went through Geryon's side hitting all three hearts at once, killing Geryon.

• Ghoul - The Ghouls serve as security guards in the Underworld and make a sound that is similar to bats. They escort the souls of the wicked to the Fields of Punishment as seen in "The Lightning Thief" when they take a preacher who had been scamming people there.

• Giant Badger - A giant badger. In "The Last Olympian," it was mentioned that Gleeson Hedge tried to fend off the Giant Badgers and tried to summon Pan to help him to do that.

• Giant Crab - A giant crab that might be Cancer. Percy fought it in the Princess Andromeda during his mission with Charlie. He defeated it by stabbing the soft tissue on its belly.

• Giant Scorpion - A giant-sized scorpion. Daedalus (under the alias of Quintus) ordered some Giant Scorpions from Triple G Ranch and kept them in their boxes in the Sword Fighting Arena. He eventually let them out in the camp's forest for a game.

• Giant Snake - A large snake that might be Python. It attacked Tyson and Grover when they were in the Labyrinth as seen in "The Battle of the Labyrinth."

• Giant Squid - A giant squid that might be the Kraken. It was among the sea monsters in Oceanus' army.

• Gorgon - A Gorgon is a female humanoid creature with snakes for hair. Anyone who looks at the face of the Gorgon Medusa turns to stone.
  • Medusa - The Gorgon who is the sister of Stheno and Euryale. Under the moniker of "Aunty Em," she attempted to lure Percy, Annabeth, and Grover into a false sense of security and turn them into stone statues. She is defeated, and her severed head is mailed to the gods of Olympus as proof of the trio's courage (though Grover notes that it is more akin to impertinence). Percy's mom uses her head to turn Gabe Ugliano to stone. In the film adaptation, Medusa is played by Uma Thurman.
  • Stheno - A Gorgon who is the sister of Medusa and Euryale. In "The Lost Hero," she was mentioned to be among the characters who were brought back to life when the Doors of Death opened. Stheno is later found to be chasing Percy (with her sister Euryale) and is described by Percy as appearing as a dumpy old grandmother but with rooster feet and bronze boar tusk sticking out of the corners of her mouth.
  • Euryale - A Gorgon who is the sister of Medusa and Stheno.

• Gray Sisters - The Gray Sisters are women who share one eye and one tooth. In "The Sea of Monsters," Percy, Annabeth, and Tyson run into the Gray Sisters who are in the form of three taxi drivers. During the Gray Sisters' argument, Percy manages to grab their eye and demand the location of which they had mentioned. They tell him 30, 31, 75, 12 which Percy didn't understand. He however gave the eye to Wasp and they drop the three off at Camp Half-Blood. Later at the campfire, Percy figures out that the numbers were used for longitude and latitude which leads to the Sea of Monsters. In the film adaptation, the Gray Sisters are played by Mary Birdsong, Yvette Nicole Brown, and Missi Pyle.

• Griffin - A Griffin is a creature that is part eagle, part lion. They appear in The Son of Neptune where they are seen in Alcyoneus' camp.

• Harpy - Aello ("storm swift"), Celaeno ("the dark") – also known as Podarge ("fleet-foot") – and Ocypete ("the swift wing") are the three Harpies that were created by Zeus. They work in Camp Half-Blood as "the cleaning harpies" being allowed to eat any camper who stays in camp past noon in the last day of the summer without completing their form. The Harpies also cleaned the dishes with super-hot lava and are also good in mid-town traffic. Though the harpies have been used to torture the wicked by stealing their food and not letting them sleep.
  • Ella - Ella is a Harpy who appears in The Son of Neptune. She has red hair and feathers, grey eyes, and a bony structure. She has extensive knowledge about the Romans and their culture. Ella is very valuable to the enemy side as she might have knowledge of several scrolls of prophecies. She has memorized a lot of books, and often recites a few prophecies from the Sybilline books that Octavian desperately wants. It is mentioned towards the end of The Son of Neptune, that Ella needed to be hidden from Octavian because of this important knowledge. She was one of the Harpies who was trying to torment the blind psychic Phineas. Near the end of the book, it is revealed that Tyson has a crush on Ella and that she has a crush on Tyson. Because of this, Ella remains with Tyson at Camp Jupiter.

• Hekatonkheires - The Hundred-Handed Giants of incredible strength, superior even to the Cyclopes. They are taller than mountains. The last one, Briares, was imprisoned by Kampê in the fourth book. It is mentioned that his brothers, Cottus and Gyges, have faded because people have forgotten about them. When Tyson finds that Briares (his hero) is too afraid to escape, he is heartbroken. At the end, Briares returns to help defeat Luke and the Titans. In The Last Olympian, Percy sees Briares helping Poseidon defeat the forces of Oceanus.

• Hellhounds - Hellhounds are a main part of Luke's army and monsters in general. They are described as very large black dogs that have fire glowing in their eyes. They were also mentioned to reside in the Fields of Punishment. Daedalus owns a hound named Mrs. O'Leary, who, unlike her relatives, is loving and loyal. In "The Last Olympian," a bunch of Hellhounds are seen in Kronos' army where they snuck behind the demigod lines.
  • Mrs. O'Leary - Mrs. O'Leary is the only friendly hellhound to ever exist. Quintus (an alias of Daedalus) was her original owner, but, after asking Nico Di Angelo to kill him, Percy becomes the hellhound's owner. While Percy is in the "mortal world", Charles Beckendorf takes care of her at Camp Half-Blood. She rescues Percy while in the Labyrinth.

• Hippalectryons – The Hippalektryons are an endangered animal that is part chicken, part horse. In "Battle of the Labyrinth," they are seen at the Triple G Ranch.

• Hippocampus – Hippocampi are horses from the waist up with a fish tail from the waist down. One is said to take a liking to Tyson, and he named it Rainbow. They are also called "fish ponies" by Tyson.
  • Rainbow - A Hippocamus who befriends Tyson in "The Sea of Monsters. Loves to give Tyson rides all over the sea.

• Hyberboreans - A race of ice giants who freeze into ice when defeated. They side with Kronos in The Last Olympian. They can also freeze object and people using their frosty breath.
  • Morrain - A Hyperborean who appeared in The Last Olympian. He was a part of a truce meeting.

• Hydra - A monster with nine heads. Every time a head is chopped off, two new heads grow back. This monster appears in The Sea of Monsters where its life force is linked to the Monster Doughnut Shop, as another one pops up every time the Hydra regrows a head. It was destroyed by the cannons of the CSS Birmingham. In The Lightning Thief film, the creature takes the form of five janitors (played by Tom Pickett, Keith Dallas, V.J. Delos-Reyes, Spencer Atkinson, and Tim Aas) in the Parthenon replica in Tennessee and refers himself as "We." They Hydra is ultimately defeated by the use of Medusa's head.

• Ichthyocentaur - The Ichthyocentaurs are creatures that have the upper bodies of men, the lower fore-parts of horses, ending in the serpentine tails of fish. Their brows were adorned with a pair of lobster-claw horns. In The Mark of Athena, the demigods encounter the Ichthyocentaurs who save them from Keto and her children. The Icthyocentaurs also run Camp Fish-Blood for Merpeople heroes.
  • Aphros - An Ichthyocentaur who is the half-brother of Chiron. He teaches home economics.
  • Bythos - An Ichthyocentaur who is the half-brother of Chiron. He teaches fighting.

• Kampê - A snake-haired, centauroid creature who is half-woman, half dragon, with wings and the heads of various mutated wild animals growing from her human torso. She is a monster who imprisoned the Hundred-Handed Ones and Cyclopes during the First Great War. She is feared by all, and is defeated by Briares in the "Battle of the Labyrinth" by being crushed by boulders.

• Karpoi - The spirits of the grain who are the size of toddlers. In "The Son of Neptune," Percy Jackson, Hazel Levesque, and Frank Zhang encounter three Karpoi.

• Keres - The Keres are battlefield spirits of famine and disease who feed on violent deaths. They reside in the Underworld and support the Titans but do not assist them in "The Last Olympian." In "The Demigod Files," some of them attacked Percy, Thalia and Nico and one of them poisoned Percy. "Bob the Titan" managed to heal him.

• Ketos - Chiron mentions this giant sea monster in "The Titan's Curse".

• Ladon - Ladon is a giant dragon who is one of the offspring of Echidna. It defends the Hesperides' apple tree. Ladon poisons Zoë Nightshade in The Titan's Curse.

• Laistrygonians - A race of muscular cannibal giants who serve as the brawn of Kronos's army as seen in "The Sea of Monsters." Three of them infiltrated Percy's school as visitors from Detroit and attacked the students with flaming dodgeballs. They were defeated by Percy, Annabeth, and Tyson. In "The Battle of the Labyrinth," a Laistrygonian assisted Kelli the Empousai into capturing Percy, Annabeth, and Rachael where they were marched to Antaeus' lair. Two more Laistrygonians were seen in Daedalus' lair where they followed Minos and carrying Nico with them. When the Titan army made their way through the Labyrinth and attacked Camp Half-Blood, the Laistrygonians were among the monsters that took part in the attack. They were pushed back by the campers in Apollo's cabin and the Laistrygonians retreated when Grover unleashed the powers of Pan. In "The Last Olympian," The Laistrygonians were seen in The Battle of the Labyrinth. When one Laistrygonian tried to attack Sally Jackson, she managed to shoot it.
  • Joe Bob - A Laistrygonian.
  • Marrow Sucker - A Laistrygonian.
  • Skull Eater - A Laistrygonian.

• Lamia - Lamia is the daughter of Hecate who was one of the former love interests of Zeus until Hera turned her into a monster after the death of her children. In "The Demigod Diaries" story titled "Son of Magic," Lamia is revived by Gaia to kill Hecate's son Alabaster Torrington. Alabaster manages to defeat Lamia until Hecate arrives to save both her children. According to Hecate, Lamia won't try attacking Alabaster again, knowing he could use that spell against her.

• Leviathan - These are mentioned by Poseidon in "The Last Olympian" as sea giants neutral in the war between Poseidon and Oceanus.

• Lotus-Eaters - A number of them run the Lotus Hotel and Casino in The Lightning Thief. The hotel is filled with arcade games that makes visitors not want to leave. They are also mentioned in the Odyssey by Homer.

• Maenad - A bunch of Maenads appeared in The Demigod Diaries story "Leo Valdez and the Quest for Buford." They were seen skipping in a mall-shaped clearing in the Camp Half-Blood Forest where a Drakon appeared. They managed to easily rip it apart with their long white talons and their elongated wolf-like fangs.

• Manticore - This monster has a human face and the body of a lion, as well as a scorpion's tail. A Manticore appeared in The Titan's Curse in the form of Dr. Thorn, the vice principal of Westover Hall (the school that Bianca and Nico di Angelo attended). He has two eyes of different colours, one blue and one brown. His nostrils flare up when he talks. He speaks in a French accent. He is angry that in the ancient days, the Gods forced him to live out in Persia, where he never had any decent challenges, as he would in Ancient Greece. He is killed by Dionysus.

• Merpeople - A race of sea creatures that are half-human and half-fish. The male merpeople are called Mermen while the female merpeople are called Mermaids. In "The Last Olympian," Percy wakes up underwater near Atlantis where he sees various Merpeople in battle armor fighting the forces of Oceanus. There were even some Merpeople making graves for the Merpeople who fell in battle. They serve Poseidon.
  • Bill - A merman that was trained at Camp Fish-Blood by Aphros and Bythos.

• Minotaur - The Minotaur is part-man, part bull. The monster of the labyrinth who chased Percy all the way to Camp Half-Blood. Percy defeats the monster atop Half-Blood hill and claims its broken horn as a spoil of war. The Minotaur returns in The Last Olympian as a general for Kronos's army at Williamsburg Bridge and now wearing armor. It was defeated by Percy again. In the film adaptation, the Minotaur's head resembles a Cape Buffalo's head.

• Myrmekes - A race of giant ant-like creatures who like shiny things like gold. In "The Demigod Files," some Myrmekes trapped Charles Beckendorf in their nest.

• Naiads - Nature spirits that inhabit streams and rivers and lakes, or any fresh body of water.
  • Brooke - Naiad that inhabits the brook in Camp Half-Blood. Gave a warning to Leo, Piper and Jason about her "Crazy Cousins" in The Quest for Buford.

• Nemean Lion - A lion that is one of the children of Echidna and Typhon. Luke and Atlas sent the Nemean Lion to the National Air and Space Museum to stop the group of questing Hunters and Demigods. It battled with Percy Jackson, but was hard to defeat because of its bulletproof and sword-proof pelt. Percy eventually defeated it by throwing astronaut food into its mouth thus exposing its one unprotected surface, its mouth.

• Ophiotaurus - A half-cow/half-snake monster. It is an ancient creature which could bring down the gods if it were slain and its entrails were sacrificed on a brazier. It was nicknamed Bessie by Percy Jackson who initially assumed it was female, although Grover later informed him that it was a male. Percy saved it from a trawler's net after being fetched by the Hippocampi.
  • Bessie - Bessie is the Ophiotaurus Percy meets in "The Titan's Curse." Percy named it because of its bovine appearance, but it was in fact a male. Bessie was supposedly the creature that Artemis was hunting because it could destroy Olympus. She also briefly appeared in "The Last Olympian" where Percy sees him in an aquarium.

• Orthrus - A two-headed dog owned by Geryon and brother to Cerberus.

• Pegasus - Pegasi are winged horses, named after the original mount of Bellerophon.
  • Blackjack - He is the pure black Pegasus and Percy's loyal friend. He is first introduced in the second book The Sea of Monsters on the Princess Andromeda, Luke's demon cruise ship, where Percy rescued him from Kronos's minions. Ever since then, Blackjack has felt like he has to pay Percy back for saving him and he does whatever Percy asks calling him "boss".
  • Guido - A light gray(white) Pegasus who is friends with Blackjack. In "The Last Olympian," Guido and Porkpie aided Percy and Blackjack in the Battle of Manhattan.
  • Porkpie - A light gray(white) Pegasus who is friends with Blackjack. In "The Last Olympian," Guido and Porkpie aided Percy and Blackjack in the Battle of Manhattan.
  • Scipio - Reyna's Pegasus who appears in The Son of Neptune. His nickname is "Skippy" because he's the color of peanut butter (the same color as chestnuts).

• Peleus - A dragon that is now guarding the Golden Fleece which hangs on the tree that Thalia was previously within. He is possibly named after Peleus: Father of Achilles.

• Pit Scorpion - A deadly type of scorpion that appears in "The Lightning Thief." When Luke brings Percy into the woods and reveals his allegiance to Kronos, he summoned a Pit Scorpion to attack Percy. He tells Percy he should not go for his sword, as the pit scorpion can kill in sixty seconds, and can jump up to fifteen feet. When Luke disappears, Percy manages to kill it even though it managed to sting him. Wood nymphs help Percy recover from its poison.

• Satyr - Half man, half goat. Most of the Satyrs work at Camp Half-Blood. Their Roman counterpart is a Faun. Grover Underwood is a satyr.
  • Gleeson Hedge - Percy Jackson finds a letter addressed to Grover Underwood in "The Last Olympian" where he tried to summon Pan's spirit to help fend off some giant badgers. He played a major role in The Lost Hero, posing as a football coach at a school for troubled kids. He is the protector of Leo Valdez and Piper McLean
  • Ferdinand - Ferdinand is Grover's uncle who was one of the victims of Medusa in the Garden Gnome Emporium. When Kronos' army was hiding out there in "The Last Olympian," his statue form is now missing an arm and has graffiti on it without Medusa to watch over it.
  • Leneus - Leneus is a member of the Council of Cloven Elders. He is killed in The Last Olympian and is reincarnated as a laurel. He hates Grover and thinks he is a liar. When he dies, Grover takes his place in the Council of Cloven Elders.
  • Maron - Maron is a member of the Council of Cloven Elders. He only appears in book four, when he, Silenus and Leneus try to exile Grover because they think that Pan, the god of the wild, is still alive and Grover is lying about his death. He and the other members of the Council are described as being old and fat satyrs.
  • Silenus - Silenus appears in books four and five. He is the leader of the Council of Cloven Elders and is shown to hate Grover, calling him an "outcast" and a "liar" and that he has suspicions that Grover is a spy.

• Scylla - One of the two monsters (the other being Charybdis) who live on either side of a narrow channel of water in The Sea of Monsters. Should a ship sail too close to her, she uses her six heads to pluck off crew members on deck and devour them. According to Clarisse (daughter of Ares), if the crew hid below deck, Scylla would just pick up the whole boat and crush it.

• Scythian Dracaenae - A race of humanoid females with twin snake tails in place of legs. They make up a considerable portion of the Titan Lord's forces. In "The Sea of Monsters," Percy first encounters them on the Princess Andromeda. In "The Titan's Curse," some Scythian Dracaenae attacked Percy's group after he had defeated Atlas. In "The Battle of the Labyrinth," Percy fights a Scythian Dracaenae in Antaeus' lair. Percy almost immediately kills it much to Antaeus' disapproval. The Scythian Dracaenae also show up in the actual Battle of the Labyrinth as one of the main types of soldiers. In "The Last Olympian," the Scythian Dracaenae are seen taking part in the Titan Army's attack on Manhattan.
  • Queen Sess - The Queen of the Scythian Dracaenae who appears in "The Last Olympian." She fought Chiron alongside Kronos and was killed when Chiron fired one of his arrows in between Queen Sess' eyes.

• Sea Serpent - In "The Last Olympian," a sea serpent was seen amongst the sea monsters in Oceanus' army. Deimos is seen riding one in "The Stolen Chariot."

• Sirens - The Sirens are dangerous bird women whose sweet songs lead many sailors to their deaths on the jagged rocks. In The Sea of Monsters, they almost kill Annabeth.

• Skeleton - Skeletons are the troops that make up Hades' Undead Army. In "The Lightning Thief," Hades has skeletons in army uniforms guarding his palace. In "The Battle of the Labyrinth," Nico manages to employ them as part of a ritual that will enable him to call the spirit of his sister to speak with her. In "The Last Olympian," Nico and Hades manage to bring a troop of skeletons to help fight the Titans. They are later seen constructing a cabin at Camp Half-Blood which is dedicated to Hades.

• Skolopendra - A sea monster that is 200 ft. long. It looks like a cross between a giant shrimp and a cockroach with a pink chitinous shell, a flat crayfish tail and millipede-type legs. Its face is a slimpy pink like an enormous catfish with two glassy dead eyes and a gaping toothless maw. It has a beard which has a numerous amount of tentacles sprouting from each nostril. In The Mark of Athena, Ceto sents Skolopendra after the demigods after their escape from Phorcys' aquarium. It attacked the Argo II when Leo forgot to turn the monster-detection system on. Percy describes Skolopendra as "shrimpzilla." Skolopendra withdraws into the ocean when Leo Valdez and Hazel Levesque throw test tubes filled with Greek Fire into its mouth.

• Spartus - A troop of skeletons armed with weapons. They are usually summoned by planting dragon teeth in the ground and watering them. In "The Titan's Curse," some spartoi ambushed Percy, Thalia, Zoe, Grover and Bianca in New Mexico. Due to her being a child of Hades, Bianca managed to destroy them.In "The Son of Neptune," Frank (as a gift from his father) is given a spear with the tip of a dragon's tooth that when planted with raise a Spartoí, he uses this to defeat the basilisks outside of the R.O.F.L. head quarters, to kill some of the laistrygonians surrounding his grandmothers house then using his final charge to protect the mortals on a train from attacking Griffins.

• Sphinx - A Sphinx is a monster with the head of a woman and the body of a lion. Percy Jackson and his friends encountered the Sphinx while navigating the labyrinth. Rather than tell riddles, the Sphinx asked historical questions which Annabeth refused to answer as an insult to her intelligence.

• Stymphalian Birds - A flock of birds once attacked Camp Half-Blood in The Sea of Monsters. Percy and Annabeth used Chiron's music to scare them so Apollo's cabin could shoot them down.

• Sybaris - In "The Titan's Curse," Atlas used her teeth to create spartoi.

• Talos - Talos is a giant automaton. Percy, Thalia, and Bianca fight a prototype of Talos in the Junkyard of the Gods. Apparently, he has a manhole at the base of his foot for 'servicing'. Bianca went in to mess up his circuit so they could deafeat him. He fell on some power lines thus electrocuting Bianca.

• Telekhines - A race of dog-faced sea demons that reforged Kronos's blade in the fourth book. Some set Percy on fire in the fourth book. They also appear in the fifth book. In the fourth book, they are referred to as "telekhines." However in the fifth book, they are referred to as "telkhines", without the second "e". This may be a typographical error or something different of the author's choice.

• Trojan Sea Monster - A type of sea monster that rampaged the coasts of Troy until it was slain by Heracles. It is also known as the Keto Trois. In "The Lost Hero," Jason Grace claims to have slew this monster, while fighting King Porphyrion of the Gigantes.

• Typhon - A very powerful monster. He sired many monsters by Echidna. He lives and sleeps inside Mount Saint Helens. Percy is such a powerful demigod that he almost wakes Typhon during his visit there. In The Last Olympian, Typhon awakes and moves across America destroying everything in his path. As he is concealed in mist, Typhoon's appearance is not described and appears as a freak storm. The gods of Olympus try to stop him, but he is too powerful. In the end, Poseidon and his army help defeat him where Poseidon opened up a tunnel that sends Typhon into Tartarus. Once Typhon was defeated, a wave of anemoi thuellai were born.

• Unicorn - A horse with one horn. A herd of Unicorns are used as steeds for the campers of Camp Jupiter. A red-tinted Lares with the head of a wolf guards them.

• Venti - A race of storm spirits that were born when Poseidon opened a tunnel that sent Typhon into Tartarus. Depending on how chaotic they are, Venti can appear as either smokey men with angel-like wings or smokey horses. In "The Lost Hero," Aeolus sent the Venti to prevent Jason, Piper, Leo, and the Hunters of Artemis from rescuing Hera. Their Greek counterparts are anemoi thuellai.
  • Dylan - A ventus that was among the Venti that attacked Jason Grace, Piper McLean, and Leo Valdez as seen in "The Lost Hero."
  • Tempest - A ventus in smokey horse form that appears in "The Lost Hero." Grace tames Tempest so that it can help him fight Porphyrion. He is shown on the cover of The Mark of Athena with Jason riding him, but it isn't official that that is actually Tempest

• Werewolf - A werewolf is a creature that is part man, part wolf. In "The Lost Hero," King Lycaon led a pack of werewolves to kill Valdez and McLean. Most of the werewolves were defeated by the Hunters of Artemis.

• Zombie - A bunch of Zombies were seen as passengers on the Princess Andromeda in The Sea of Monsters. Clarisse used the zombies of Confederate soldiers to operate the CSS Birmingham.