Characters: Devious Diesel, Iron Arry and Bert, Splatter and Dodge
All five diesels were built in 1953.
Diesel came to Sodor in 1961, and caused problems for the other engines. He almost managed to scrap Thomas, Percy, Toby and Emily (because of Emily's stupidity) and destroy Henry for being a failed experiment. He later returned in 1982, and tried to destroy Emily, but almost managed when Boco saved Emily from scrap. In 2005, he tried to destroy steam engines with Diesel 10, but was defeated when he, Arry and Bert were pushed into a bank of garbage.
Arry and Bert
Arry and Bert came to Sodor in 1972. In 2002, they and Diesel tried to ruin the Christmas party, but failed badly. They tried to destroy steam engines in 2005, but were outwitted when they were pushed into a bank of garbage.
Splatter and Dodge
Splatter and Dodge came to Sodor in 2005 along with Diesel 10 and Alfred. They had Daisy and Mavis trapped, but they soon chased down James and Dennis.
Splatter was diverted into a siding, derailed, and a tree crushed him flat. Dodge almost made James into rusty red scrap iron, but fell off the tip, and smashed to pieces. Both diesels were soon scrapped after that.
Diesel is, in essence, the average pantomime villain. He is oily, malicious, devious, scheming and full of ideas to get revenge.
Arry and Bert are unquestionably devious and scheming.
Splatter and Dodge both were fairly simple-minded and tend to banter. Splatter was the more talkative of the two, while Dodge was more intelligent.