Diesel is a robot who needs voice boxes to communicate or make noises from his mouth. His personality changes to suit the voice box he is currently using. Some of the personalities he uses include those of a dog, a singer, a cowboy and Darth Vader. He and his friends often look for voice boxes that he can use. A running gag throughout the movie involves him finding and trying to use different voice boxes, then acting out a pop culture reference for each one. For example, when hearing about Rodney's talent, he assumes a voice box and says "The Force is strong in this one" in Darth Vader's voice. In the end, Diesel receives a brand-new voice box from Bigweld, and starts singing like James Brown. He also wears shoes.