Diesel is a diesel engine who lives on Sodor with Thomas and his friends. His best friends are Thomas, Percy, Nia, Kana, Carly, Sandy and Bruno.
Personality
Unlike the original series, where he was oily, malicious, devious, scheming, and full of ideas to get revenge, Diesel is portrayed as one of Thomas' best friends. He is Thomas' competitive friend, always trying to one-up Thomas, and inadvertently causes trouble for everyone in his quest to be "the real Number One Engine." However, he does still retain some of his original personality, like teasing others, and trying to sabotage others in order to win a race. But despite this, he still has his limits when it comes to sportsmanship, especially after he witnessed his favorite racers, Farona and Frederico try and sabotage Thomas and Kana's chance at winning the Sodor Cup.
Diesel's favorite object is an old, rusted oil can he named Rusty. Despite it being dirty and noisy, he keeps it around for sentimental value.
Technical Details
Basis
Diesel is based on a British Rail Class 08 diesel-electric shunter. In the real world, BR Class 08s were in fact the most successful shunting engines in the world with 996 of them built. Over seventy of them are preserved by heritage railways, such as the Dean Forest Railway and museums, such as the National Railway Museum. Around one-hundred BR Class 08s also remain in service on the national rail network.
BR Class 08
Livery
Diesel is painted mostly black with a deep purple stripe along his side as well as a deep purple running board and wheels. His bufferbeam is painted red.
During Race for the Sodor Cup, Diesel briefly wears a special livery in support of Farona and Frederico which is similar to his normal livery, however with a few notable differences. Namely, his running board and the stripe along his side are yellow, with an additional orange stripe in the middle and a yellow box under his face. After witnessing them cheat in an attempt to preserve their chances at winning, Diesel reverted back to his normal livery after Kana and Thomas crossed the gap. However, Diesel does have his special livery again in the Let's Race videos, The Egg Race and The Bell Race.
Since his last appearance in Thomas & Friends, Diesel has had notable changes:
His forehead is now much larger.
His cab doors have been re-designed.
His cab windows have been removed.
He now has purple irises.
He lacks his outside frames.
His nose is more rounded off.
His brake pipe has been removed.
He is diminutively smaller.
His back stepladder have been removed, while his front stepladders retain a different design.
He has gained a running board.
The handrails on his cab have been removed.
He now has grilles on the rear of his cab where his front windows used to be.
He has a new horn which is a stock sound effect.
He no longer speaks with a British accent in the US dub.
Unlike the original series, Diesel is a part of the main cast of engines, and instead of being an antagonist, he is portrayed as one of Thomas' best friends and now lives at Tidmouth Sheds with the other engines.
In an early storyboard demo of the fourth season episode, Quacking Quandary, Diesel was originally portrayed with a winch the can emerge from the front of his footplate. But this later cut in the final draft.
Due to All Engines Go straying away from railway realism, Diesel is now incorrectly referred to as a "tank engine". This may be justified if it refers to his internal diesel tanks.
Diesel was the first character to have their voice actor recast in the US dub; the previous recastings happened in the UK dub.
In the Polish dub, Diesel is called both "Diesel" and the mollification of his name "Dieselek".
