"Devious" Diesel, as his name implies, is a sinister diesel shunter and the first diesel engine to arrive on Sodor who originates from the Other Railway. In the television series, Diesel is a permanent resident of Sodor.
Diesel is, in essence, the average pantomime villain. He is oily, malicious, devious, scheming and full of ideas to get revenge. He views himself and any other diesel of his kind as highly above the steam engines, and believes that all diesels are "revolutionary". However, despite his antics giving diesels on Sodor a bad reputation, which causes most steam engines, particularly Duck and Thomas, to mistrust him, he still wants to prove himself to be a really useful engine. He is also very proud to be the first diesel on Sodor.
Diesel is a BR Class 08 0-6-0. Over seventy members of this class survive today in preservation. They were in fact the most successful shunting engines in the world, with 996 of them built. The Diesel Shunter, Splatter, Dodge, 'Arry, Bert, Paxton, Sidney and The Great Railway Show Diesels are also members of the class.
Diesel is painted in the black livery used by British Railways for shunting engines in the 1950s. His siderods were silver until the sixth season and have been black in every season after.
- Season 100 - Diesel Saves the Day, Samson's Waste Dump, Jealous James (cameo), and Sidney Helps Out (cameo)
- The Return of Sailor John (cameo)
- Kerry Shale (UK; thirteenth season onwards, US; nineteenth season onwards)
- Michael Brandon (US; thirteenth season - Blue Mountain Mystery)
- Martin Sherman (US; King of the Railway - eighteenth season)
- Jorge Ornelas (Latin America; thirteenth season onwards)
- Daisuke Gōri (Japan; second - eighth seasons, excluding the sixth season)
- Hisao Egawa (Japan; sixth season only)
- Ken Sanders (Japan; Calling All Engines! onwards)
- Paweł Galia (Poland; thirteenth season only)
- Janusz Wituch (Poland; Misty Island Rescue onwards)
- Christoffer Staib (Norway; thirteenth season - sixteenth season, excluding Day of the Diesels, Blue Mountain Mystery and King of the Railway)
- Helge Winther Larsen (Norway; Day of the Diesels onwards)
- Martin May (Germany; thirteenth season onwards)
- Christian Rudolf (Germany; Audio Books only)
- Reinder van der Naalt (The Netherlands)
- Anibal Munhoz (Brazil)
- Jorge Teixeira (Spain)
- Michel Lasorne (France and French speaking Canada; eighth - twelfth seasons)
- Fabrice Trojani (France and French speaking Canada; thirteenth season onwards)
- Gadi Levy (Israel)
- Dor Srugo (Israel; King of the Railway only)
- Petri Hanttu (Finland; Misty Island Rescue onwards)
- Quổc Tín (Vietnam)
- Alexander Kotov (Russia)
- Bohdan Tůma (Czech Republic; Blue Mountain Mystery onwards)
- Diesel was the first diesel to be introduced in both the Railway Series and Television Series.
- According to the magazines and the DVD Bingo game, he and Bulgy are good friends.
- Between the thirteenth and sixteenth seasons, Diesel was the only character from the model series to still be voiced by the narrator in the CGI Series, though this was only in the US narration.
- Diesel has had a few modifications in the television series:
- Season 6:
- His siderods changed from silver to black.
- His brakepipe began facing upwards.
- Misty Island Rescue:
- His horn sound changed to that of a generic diesel, sounding more like an "American" diesel.
- Day of the Diesels:
- His horn sound changed back to how it originally sounded.
- Season 19:
- He gained a light above his face.
- His coupling chain became red.
- He gained a permanent tail lamp.
- Season 20:
- His coupling chain changed back to black.
- Season 6:
- In some merchandise lines he is referred to as "Devious Diesel". It was not until Fergus Breaks the Rules that he was referred to by this name onscreen.
- Diesel has travelled at well over his top speed of 20 miles per hour on numerous occasions.
- Diesel's face in the magazine stories is often smaller than in the television series.
- Nathan Clarke did an audio sample for Diesel on his DAA Management Page.
- Diesel is the fifth character to break the fourth wall: the first was Stafford, followed by Paxton, Rocky and Percy.