Plesio (Voiced by Dan Hennessey) is an evolved Plesiosaurus, a prehistoric aquatic reptile contemporary to dinosaurs but nevertheless not related to them. He is extremely cunning and shifty. He resembles a pink dragon, having a small crest atop his neck and a triply split salience at his chin. He is a member of the Tyrannos, and is the evil counterpart of Ichy.
Like Ichy, Plesio can also talk to sea creatures. Unlike his Dinosaucer equivalent, however, he uses this ability to convince them to mistreat mankind and everything related to them.
Plesio used to work for Slither, Slither and Shark, Attorneys at Law before he became a Tyranno. He once had a romantic and reciprocal relationship with the Loch Ness Monster, also known as Nessie, who is an Elasmosaurus. However, he was forced to leave her to guarantee her safety from the Tyrannos. He rarely shows this sort of noble nature, and even the Dinosaucers were stunned to see it in him.He serves as the scientist/inventor of the group, creating most of the gadgets and machines used by the Tyrannos. He is creative and inventive but his inventions, such as the Defector Ray, usually backfire..This, combined with the low success rate of the Tyrannos, leads his labors to be quickly discarded and junked. Plesio, however, is optimistic. He also sometimes conducts his plans apart and separate from the other Tyrannos, in favor only of his own personal gain. This is often in contrast to Genghis Rex´s commands.
Plesio’s spaceship superficially resembles a plesiosaurus. Like Ichy’s ship, Plesio’s moves as freely in the water as it does in air and space. The “neck” of the ship is flexible-- thus giving the cockpit a free range of motion, perhaps increasing the visual field.
- Plesio draws out all his 's' sounds, making him speak like a snake is often depicted in animated media.
- An action figure of Plesio was planned by toy company Galoob, but was cancelled. When the toyline was released by Glasslite, Plesio is one of three characters who had a prototype but was not produced.