Diesel Springer is a supporting character and the comic-relief character in Robots. He was voiced by Charles Nelson Reilly, but speaks for brief moments during the film using the voices of a Spanish-speaking football commentator, a dog, Darth Vader, Sally, Dr. Finklestein, an opera singer, a wrestling announcer, and James Brown.
Diesel is a small, dark blue robot with bright green eyes, which seem to have glass over them as shown when they randomly shatter when Madame Gasket says she's a woman. He has a small body with long arms and legs, and a very large, flat head. He has what appears to be some sort of dial for a nose, and two switches atop his head that he uses as an instrument towards the end of the movie before singing. He appears to have a light pink tongue. During the final fight, he is "upgraded" to look like a cowboy.
Diesel is a fun-loving, silent/mute, anxious, gentle, happy-go-lucky, deaf, comical, laid-back, funny, kind and often unintelligible character. Whenever he is given a voice box, Diesel's personality seems to alter, which is first shown when Lug gives him one to make him sound like what seems to be a over-excited sports' announcer and causing him to become crazy such as whacking Lug in the chest and running in circles until he is tripped by Lug. He then acts like a dog, growling at Crank Casey when he tries to remove the voice box and even gaining "puppy-dog eyes" and sticking out his tongue. Diesel is missing a voice box, meaning he cannot speak. However, whenever he puts a new voice box in, he gains a matching personality. For example, after Lug unknowingly gives him a dog's voice box, he begins to bark like a dog and growls at Crank. Diesel lives with Aunt Fanny, Fender, Piper, Crank and Lug at the boarding house. At the victory celebration in Rivet Town, Bigweld gives him a new voice box, which causes him to gain the singing voice of James Brown. After using the two switches on his head as an instrument, he proceeds to sing "Get Up Offa That Thing" as the rest of the characters dance along.
Diesel first appears with Fender Pinwheeler at the train station, trying to scam Rodney Copperbottom out of his money. He seems to function as a cash register at that point. In the next scene where Fender and Rodney are riding to Bigweld Industries, Diesel does not appear with Fender.
He appears a few minutes later with Crank and Lug looking for parts when he and Lugnut try two voice boxes for him, revealing his name and that Diesel is mute. Just as Diesel gets a dog voice box, Fender enters the area. When Fender tells the others that Rodney intentionally knocked his head off, Diesel and Crank surround him possibly planning to attack him, but him and Crank are presumably stopped by Piper Pinwheeler.
In Jackhammer's Hardware, he appears in the background with the other Rusties. He backs up Piper when she scolds Jackhammer for not having parts for Fender and takes on a Darth Vader voice box, a Sally voice box, and a Dr. Finklestein voice box when Rodney tells Fender he can fix him.
He appears with the other Rusties going to bid Rodney farewell. But they are stopped by Bigweld. When they stop at Bigweld Industries for Bigweld to fire Phineas T. Ratchet, Bigweld tells Lugnut, Crank, Diesel, Piper, Fender and Aunt Fanny to stay and "watch Daddy's limo." But later, Diesel is shown partying in the front seat of the limo with Crank, Fender and Lugnut poking themselves out from the top of the limo, chanting "Road Trip!", to Piper's annoyance. When he notices Rodney in trouble, Diesel is the one driving the limo.
He upgrades to resemble a cowboy and wields two gun-like weapons. He also helps Lugnut at one point in the battle.
At the end, he, along with Piper, Lugnut, Crank and Wonderbot, he assists turning Herb Copperbottom's trumpet playing into a street rave. Bigweld hands Diesel a box containing a James Brown voice box for himself. He then grabs the microphone and begins to sing "Get Up Offa That Thing".
- Diesel is the smallest and shortest of the Rusties with Piper Pinwheeler being slightly taller than him.
- His last name was never confirmed anywhere else but merchandise.
- Diesel's original voice is currently unknown.
- According to deleted scene, Diesel was intended to be much more of a womanizer, attempting to hook up with both Piper and Cappy.