Diesel is a vile diesel who lives at the dieselworks.
Diesel was the first diesel engine to come to Sodor and certainly created a foul reputation for himself.
After spreading lies about Duck and being sent away, he was repeatedly called upon to help as a last resort. Some of the events that occurred during his various visits was pushing a train of China Clay into the sea, falling off a pier and into a barge after failing to prove his strength, and being nasty to Fergus when he was sent to help out at the Cement Works. Since these mishaps, the Fat Controller had no choice but to permanently enlist Diesel to the fleet. Although he still continues to cause trouble, he is a very efficient worker.