Bunnicula — The rabbit with strange eating habits and vampire-like qualities, but otherwise harmless, Bunnicula came to the Monroe household on a dark, stormy night. Toby found him in the theater, which was at the time showing Dracula, and brought him home, where Mrs. Monroe brought up the clever name Bunnicula. A note was placed with Bunnicula when he was found, written in Russian, reading "Please take care of my baby." It is unknown who left Bunnicula in the theater or wrote the note, but the letter was written in a dialect that nobody except Harold could read. He is subjected to many murder attempts by Chester, who thinks that the rabbit would eventually become carnivorous. However, his "indestructible" stature proves to Chester that he cannot be killed.
Due to his young age, Bunnicula cannot talk - or at least he simply doesn't speak at any point in the series — but shows emotions all the same, such as winking happily at Harold or crying. He does exhibit the unusual ability to get in and out of his cage without using the door, and initially opens the refrigerator by himself. Instead of a rabbit's buck teeth, Bunnicula inexplicably has fangs, which enables him to bite vegetables and suck the juice out of them, similar to the method by which Dracula dines, leaving them ghostly white. In The Celery Stalks at Midnight Bunnicula, by that point put on a vegetable diet, escapes his cage due to being put in a special cage intended for use at a pet show while being left in the Monroe's garage, and escapes into the night, leaving a trail of white vegetables in his wake which Chester is convinced must be destroyed by using a stake through their hearts. Chester had learned from his mistake in Bunnicula, and chose toothpicks as his weapon of choice in this book. (How and where he was going to locate the actual 'heart' of a vegetable was never explained.) One of Bunnicula's apparent victims tries to sneak up on Harold at the end of the book, and it is left ambiguous as to whether or not Chester was playing a prank on Harold, though Chester seemed to be oblivious to the thumping noise the vegetable was making, or if this was indeed an actual attempt at an attack by a vampire vegetable.
Bunnicula, at the end of Nighty Nightmare is revealed to have produced a litter of offspring with a rabbit owned by a friend of Pete Monroe as part of a project for the novels' equivalent of the Boy Scouts. At least one of the offspring is stated by Pete as looking identical to Bunnicula, and was briefly mentioned again in Bunnicula meets Edger Allan Crow, where he was named "Sonnicula", due to his being the son of Bunnicula and carrying an identical appearance to his father. Sonnicula never made any direct appearances in the series, being referred to only twice in passing during the events in the series. In Nighty Nightmare, Chester's story implies that Bunnicula's parents were vampire rabbits who were created by a lonely vampire, though Chester may have made the entire story up as implied by revelations at the end of the novel. However Chester seems personally convinced that the story is complete truth at the time that he tells it and tells it in such a way that it resembles a ghost story, one that entrances the other characters until the truth about the subject that brought up the story is revealed. It is the closest there has ever been to an 'origin' story for Bunnicula and his apparent powers, whether or not it was concocted entirely in Chester's imagination, and the author has never produced an actual origin for him or his abilities. Nor has he ever explicitly confirmed or denied whether or not Bunnicula is vampiric outside of occasional hints in the novels by way of Bunnicula's odd abilities and physical features.
In the non-canon animated special, produced by Ruby-Spears, Bunnicula's name is written in the note itself, to avoid having the Monroes name him. The note is one of the few aspects of the novel to carry over into the animated special, as Bunnicula is found near a processing plant in the special. In the televised version, when Bunnicula goes into his vampiric form, he sprouts bat wings under his arms and his eyes turn yellow. His vampire powers include flight, hypnosis, levitation, and telekinesis. Chester's murder attempts do not take place in the special and he ultimately decides that the idea that Bunnicula is a vampire is "ridiculous", something which doesn't occur in the novels, which has a touch of irony, since Bunnicula is blatantly shown using his vampiric powers (in as far as the animated special is concerned), and Chester was correct in his belief of Bunnicula's true nature.
Howie — The carefree and sometimes slightly dim Dachshund puppy who was adopted by the Monroes from Chateau Bow-Wow, making him the newest member of the family. He was the runt of the litter and his parents, Howard and Heather, were valuable long-haired Dachshunds (whom Chester secretly suspected of being werewolves). Howie's somewhat eerie howling has not changed the cat's mind on the matter. Howie usually does not understand the seriousness of matters, thinking that murdering vampire vegetables is a game and chasing Bunnicula is a race. He did not even know what a vampire was when Chester informed him, though he does not think Bunnicula is a danger. For an unknown reason, he calls Harold and Chester "Uncle Harold" and "Pop", respectively; while Harold is perfectly comfortable with his nickname, Chester is still not used to his own. Howie's hobbies include chewing things, eating and chasing cars (which he's not allowed to do). Despite his boldness, Howie was a bit unnerved by scary stories at first, then outgrew it after the pets' adventures in Bunnicula Strikes Again! Later, he decided he wanted to try writing too, and his first drafts turn out to be pretty good- for a puppy's work.
Robert Monroe — He is the husband of Ann Monroe and the father of Peter and Toby Monroe. He works as a college professor, and his knack for reading classical literature enabled Chester to read as well. In the animated special, he is described by Harold as being a scientist, rather than a college professor, and works at the plant where Bunnicula is discovered.
Ann Monroe — She is Robert's wife and the mother of Peter and Toby Monroe. She thought up of the name Bunnicula by combining "Bunny" and "Dracula". She had previously tried to name him "Bun-Bun" and "Fluffy". Names like this seem to be a habit with her, because Harold and Chester were both called "Fluffy" for a short time. Her occupation as a lawyer makes her a good and strict mother. In the animated special, Ann is not described as having any job other than being a housewife. She also does not name Bunnicula in the special, as the name is included in the note they find with him.
Peter Monroe — The oldest of two boys who slacks off often. He's often selfish, and usually bullies his younger brother Toby and the pets, except for Bunnicula. Harold and Chester avoid him, Chester being largely indifferent, but Howie finds him intriguing, mainly because of the scary books he reads. The space under his bed is very messy, and in addition to keeping a stuffed animal named Puddikins under it for emergency hugs, many other stuff has turned up such as Oreos, dirty socks and a notebook that Harold gives Howie.
Toby Monroe – The younger brother, and much more dignified and kinder than Peter. He likes to share his snacks with Harold during his late-night readings, and is adored by Chester and Howie. He cares a lot for the pets, and was known to slip pieces of food to Harold at dinner.
Sonnicula - the son of Bunnicula. He looked just like Bunnicula and was born during Nighty Nightmare. His mother was a rabbit brought by Peter's best friend Kyle. It was not said whether he inherited his father's vampiric appetite, but he sleeps during the day, just like Bunnicula. In the last book he was adopted by Miles Tanner.
Miles Tanner (M.T. Graves) is the author of the "Fleshcrawlers" series, of which Peter is a fan. He lived temporarily at the Monroe's house when Peter won a contest allowing it. He shows interest in Bunnicula and carried his pet, Edgar Allan Crow, around. He had a pale face, long curly hair, a black cape, and was very attached to a black bag. The black bag was thought to contain Bunnicula (by Chester, of course) when Bunnicula escaped. The pets opened the bag, greatly embarrassing Miles Tanner in front of company. The contents were stuffed animals. Miles admitted that they were to train him to overcome his fear of animals. He said he was scared of dogs, cats, and people. He wanted a rabbit because a rabbit never barked at him before. Therefore, he wants Bunnicula. In the end he adopts Sonnicula, saying "It won't be Bunnicula, but it will be fine." The Monroes are greatly relieved to still keep their amazing pet. In a letter, Miles says he will marry Ms. Pickles, Peter's school librarian and they shall be neighbors. The Monroe pets changed his mind towards animals.
Edgar Allan Crow is a crow Miles adopted, found on his doorstep when he was a wounded baby. Edgar gives Miles company and Miles has said he can't do anything without him. Edgar, however, wants to go back to his own kind. He was seen courting another crow in the Monroe's place. Edgar learns to write and sends an e-mail to the Monroes.
Mrs. Marjorie Tanner (née Pickles): Peter's English teacher, who is also a fan of M.T. Graves and in fact his wife (assumedly). She first met Tanner when she brought over a cake as an excuse to meet him before he came to visit Peter's school. Soon after the Monroes received a letter from Tanner announcing his engagement to Ms. Pickles, she is assumedly now Marjorie Tanner.
Ms.(Mz.) Kipper: The principal of Peter's school