Diesel 199 was built in the early 1960s at Derby Works. In 1967, he came on trial to Sodor with another Diesel engine, Diesel 7101. D199 soon made himself an enemy of the steam engines when he claimed that "steam engines spoil our image". Vulgar noises greeted this, until Duck and D7101 managed to shut up D199.
The next day, D199 ironically failed with a train of oil-tankers at a signal box, blocking the crossing. Henry, whose regulator had already jammed, came to help. However, after D7101's ejector leaked, making him unable to pull his passenger train, Henry was asked to help him as well. Henry, with some help from 7101, was still able to move and bravely pulled 199, the oil-tankers and the passengers to the next station. The Fat Controller was not impressed, and Diesel 199 was soon sent home in disgrace. However, his companion Diesel 7101 was given a second chance.
In the magazines, Diesel 199, along with the Diesel, returned to Sodor to celebrate "Diesel Day" with the other Diesels.
D199 was pompous and rude, and sided with the general belief amongst Diesels that steam engines are inferior to Diesel power. He is blatantly arrogant, and enjoys bad-mouthing the steam engines. However, he earned the nickname "Spamcan" by a signalman after he failed pulling a train of oil-tankers, and he subsidised when the signalman jokingly threatened to cut him up with a tin opener.
D199 thought he was more reliable than the steam engines. However, one day he broke down and quickly lost his nickname "Old Reliable". In fact, everyone was rather pleased when he was sent away from Sodor back to the Other Railway.
- D199 is best friends with Trixie.
- D199 will guest star in Thomas and Twilight Sparkle's Adventures of Star Wars Episode I: The Phantom Menace.
- D199 is also a big enemy and arch rival to The Planet Trains.
- D199 is also a boyfriend with Gilda.