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Diesel 10 is the main antagonist of Thomas and the Magic Railroad.
Diesel 10 had been to Sodor a long time ago, creating problems for the steam engines. He chased down Lady - the engine who kept Sodor alive - and made her crash. In the years that followed, Lady's caretaker, Burnett Stone, took her into hiding, trying desperately, but could not bring her back up to steam.
Diesel 10 returned many years later, intending to destroy Lady for good. He brought with him two lapdogs, Splatter and Dodge, who were present when the boss was scheming. He was first seen in the movie charging past Thomas and Gordon at Maithwaite. He also dumped sneezing powder all around Tidmouth Sheds so that the wind from Harold's blades would blow it all over the place. Diesel 10 had very little success with his plans - Mr. Conductor caused Pinchy to throw him safely onto bags of flour, and during a speech on "how to stop being stupid", he caused a coal chute at The Coaling Plant to empty its contents on top of him at.
By using special coal from Sodor, Burnett Stone was able to bring Lady back to life. Diesel 10 was determined to attack her, but lost the aid of Splatter and Dodge. Burnett, Lady, and Thomas found themselves being chased by Diesel 10 over an unsafe viaduct. The center of the viaduct collapsed, and while Thomas and Lady were able to cross safely, Diesel 10 was too large and fell into a passing barge below.
Diesel 10 is an evil, conniving, bullying, and psychotic monster. He absolutely despises steam engines, and would call them taunting names like "puffball", "Tin Kettle" and "teapot" (Thomas and Toby). He is Sodor's strongest but not quite largest Diesel, his power being enforced by his slightly malfunctioning claw, Pinchy. He can use this deftly, and is even able to use it to make a sculpture. All steam engines and diesel engines fear and respect him.
- He was supposed to be the assistant to the original antagonist of the film P.T. Boomer. However, Boomer was cut after test audiences thought the character was too scary so Diesel 10 was rewritten as the main villain.