Diesel is a devious diesel shunter. Diesel serves as the secondary antagonist of the show.
Season 1 - Races (cameo), Paxton Helps Out, Bulgy the Vegetable Bus, The New Diesel Fuel, Dave the Diesel (cameo), and Toby and Jennifer (cameo)
Season 2 - Den and the Firefighter (cameo), Wobbly Wheels, Down by the Docks (cameo), and Off to the Scrapyards
Season 3 - Red Paint, The Tug (cameo), The Mail Depot, The Adventure, and Snowmen (cameo)
Season 4 - Diesel and the Barge
Season 5 - Mavis and the Late Night Track Repairs, James and Dennis (does not speak) and Percy and the Jam