Mesogog (portrayed by Latham Gaines) is the chief villain of the series. He is also Dr. Anton Mercer, Trent Fernandez's adoptive father.
Dr. Anton Mercer was on the verge of a scientific breakthrough during an experiment involving dinosaur DNA, when he was accidentally transformed into a dinosaur-like creature called Mesogog, an evil mastermind with plans to revert Earth back to the age of dinosaurs and turn the Human race into reptilian creatures like himself.
Mesogog and Dr. Mercer have distinct personalities, but share the same body in a Jekyll and Hyde relationship. Each is aware of the other's existence, but also dislikes the situation. In his Mesogog form, he is equipped with cybernetic technology and psionic powers that he uses to torture his enemies, or his allies when he is angry at their failures.
Dr. Anton Mercer has an adopted son, Trent Fernandez, who became the White Dino Ranger when he accidentally discovered Mesogog's lab while investigating his father's mysterious comings and goings.
In his world domination attempts, Mesogog was assisted by two servants, Elsa, and Zeltrax, a cyborg whom Mesogog created à la Dr. Frankenstein from the ruined body of Tommy Oliver's former associate, Terrence "Smitty" Smith. Mesogog also controls an army of cybernetic dinosaurs called Tyrannodrones which were originally created by Tommy and Anton.
Eventually Mesogog freed himself of his humanity by using a potion created by Elsa to separate out Dr. Anton Mercer. As a result, his insanity and determination increased. He also rid himself of Elsa when needing an energy supply to power his cannon. It took a bit of deception from the Rangers (using the Dino Gems as bait) to destroy the cannon and Mesogog's base. He would later reappear after the Zords were destroyed, absorbing enough energy from the Dino Gems to survive the explosion and 'evolve' into a self-replicating dinosaur-like monster, known as the Mesomonster. As the Mesomonster, Mesogog was nearly invincible. He is finally destroyed by the Dino Rangers with a giant Tyrannosaurus of energy created from the Dino Gems. In doing so, the Rangers lost all their powers for good (though Kira would later regain her powers during the events of Once a Ranger).
Dr. Mercer survived the whole ordeal, and was thankful to the Rangers (especially Tommy) at the series' end.
Mesogog appears in the Robot Chicken episode "Kramer Vs. Showgirls" voiced by Seth Green. In a "Where Are They Now" segment revolving around characters from the 90's, Mesogog works as a manager of a Wendy's.
Read more about this topic: Villains In Power Rangers Dino Thunder