Rockmobile is one of the mutant toys in Toy Story. He is the head of a praying mantis or fly stuck on the (presumably) legless body of a Combat Carl action figure which is stuck in the headless and legless torso of a Rocky Gibraltar toy controlling it with a car steering wheel. The praying mantis-headed figure can drive the body around using the arms to walk on.
In Toy Story he's first seen on Sid's workbench, along with the Walking Car, Legs, and Ducky, retrieving parts of Janie and Pterodactyl. Initially thought to be a cannibal, the mutant toys later turned out to be friendly after they fixed Buzz and repaired the Janie Doll and the Pterodactyl.
Toy Story: The Video Game
Rockmobile appears in the later part of the level "Battle of the Mutant Toys" in Toy Story: The Video Game. He, along with Legs and Babyface will attack Woody and Buzz on Sid's workbench. Using Buzz's karate chop action, they're able to escape.