Diesel is a black diesel shunter who lives at Vicarstown. He was the first diesel engine to visit the island.
Diesel was built around 1952 for shunting work in England. In June of 1957, he was brought to the Island of Sodor for a trial by Sir Topham Hatt, who was interested in trying the new diesel engine technology. He tried to impress the engines with his good manners (likely fake just to gain good attention), which worked well at first, except for Duck. Duck was suspicious about Diesel and kept a close eye on him. Diesel boasted that he was revolutionary, so Duck played a trick on him by telling him to pull some very old trucks. This did not go well at all as Diesel couldn't get the trucks to move and lost patience. The trucks fell apart and he had to help clear the mess. Duck and the other trucks laughed at him, and the latter sang rudely about Diesel's failed attempt. Eventually, Duck was kinder to Diesel but the trucks were still being horrid. Diesel now hated Duck and wanted to get rid of him, so he made a plan. He lied to the trucks that Duck had called Henry, Gordon, and James vulgar names. The trucks didn't keep this a secret, as Diesel had planned, and harassed the three engines. Henry, Gordon, and James started ganging up on Duck while Diesel acted as if he knew nothing. However, the Fat Controller knew well enough Diesel was likely involved. He sent Duck to Wellsworth so he could investigate the matter. And indeed, when Diesel started telling lies about Henry, the Fat Controller sent him back to England.
In 1991, the Fat Controller was in desperate need of another engine to help Duck and Percy in the harbor. Diesel was the only engine available for rent (likely because of his attitude, no one wanted him), so the Fat Controller decided to give him another chance. But like before, Diesel was up to no good. He bullied Duck and Percy and while trying to foolishly show his importance, accidentally banged the china clay trucks into the ocean. Like the first time, he was sent back. However, eleven years later, the Fat Controller ran into the same predicament when Henry had an accident with trucks. Diesel was given another chance, but on the first day, he ended up falling off the dock after trying to pull a massive amount of trucks to prove he was "The World's Strongest Engine." And yet again, he was sent away, however, after saving Oliver, Toad, and Salty from the burning Steamworks at Crovan's Gate, The Fat Controller decided to keep Diesel on his railway, the Class 08 changing his attitude. A year later Diesel told Fergus he was to be deposed and sent to work at the scrapyard. Fergus believed him and ran away. However, this time, the Fat Controller sent Diesel to work at the scrapyard instead of going back to England. Diesel may have apologized and made up for his actions. Also, his class were being scrapped on the mainland so the Fat Controller gave him permanent residence on the Island under certain conditions. Eventually, Diesel was moved to Vicarstown, where he now lives, and does many different jobs on the Island. He is still boastful, but not as bad as when he first arrived.
In the deep freeze of early 2014, Diesel lent some of his fuel so Donald and Douglas could be freed from the snow. Later, when he derailed after being careless, he and BoCo witnessed Neil rush by, though they did not know it was him.
In an alternate universe, Diesel hated Christmas. A Diesel 10 figure in his mind tormented him about it. After causing a dreadful accident and the hate towards him that followed, Diesel decided to steal Christmas. However, before he could destroy the items, a Lady figure in his mind convinced him not to. Diesel then regenerated into a Sodor Island 3D 2012 model, and he brought everything back.
In the majority of How the Diesel Stole Christmas, SI3D's 2006 model of Diesel was used. However, SI3D released their 2012 Diesel during filming. Thomas1Edward2Henry3 wanted to incorporate it, so he quickly wrote a scene where after being enlightened about Christmas, Diesel regenerates into the new model.
Diesel is considered the main antagonist of the show, so he is very arrogant and thinks steam engines are hideously obsolete. He can be very mean spirited, often bullying others, especially Duck, Percy, and Thomas. However, he does have a small amount of kindness, but one would have to look deep down. Diesel changed his attitude after The Fat Controller decided to keep him, and although he still despises steam engines, he can lend a helping wheel.
- Right on Traction (cameo)
- DarthWill3: How the Diesel Stole Christmas-Episode XV + Specials
- Thomas1Edward2Henry3: Episode XVIII-Present
Diesel first appeared in the second season episode Pop Goes the Diesel and appeared in every season since except the fifth. His season 4 appearance is debatable. His model was used on the "Other Railway" set in Rusty to the Rescue, but it is unknown if it is him or another black Class 08. Considering he was in England at the time, it's possible it could have been him. Diesel is voiced by Kerry Shale in the US and UK dubs. He was previously voiced by Michael Brandon until his departure after the 16th season. Diesel is the only engine to be voiced by a narrator after the 12th season.
- Diesel is considered the main antagonist of the show, especially since the eighth season.
- DarthWill3's Diesel performance is one of Thomas1Edward2Henry3's favorites of the voice actors.
- Diesel originally had an episode in NWR Origins about what happened while Duck was on Edward's Line but T1E2H3 said it would add another long episode of hard work. Diesel's scrapped episode was put into The Devious Diesel and Sent Packing.