First Appearance Trouble in the Yard
Diesel is a devious shunter who works on Sodor. 


When Duck is tasked with hauling a long special special, Sir Topham Hatt assigns Diesel to help him. Duck, who is plotting to get rid of Diesel, lets Diesel go out the front. As the pair are near a bridge over the yard, Diesel is pushed off the broken bridge by a crazy Duck.

Following Mavis' accident at the Quarry, he meets her and BoCo at the Works, fed up by Duck's actions. They band together to devise a plan with the help of newcomer Diesel 10. They confront Duck, threatening to detain him. However, Thomas, Percy, and Toby arrive, claiming Duck's actions that it is a result of being possessed. However, Toby fails to exorcise the demon, allowing the possessed Duck to escape, derailing Diesel behind Knapford Station in the process. 

While the other engines focused on helping Duck, Diesel was left derailed behind the station. After a few months and some snowfall, Diesel was rescued by Mavis and Rocky. Right as he was put back on the tracks however, an out of control Edward knocks Diesel back where he once lay.