Diesel 10 is a very mischevious diesel with a slightly malfunctioning claw on his head named "Pinchy." He absolutely despises steam engines, and would call them taunting names like "puffball" and "teapot". He is Sodor's strongest but not quite largest diesel. All engines, steam and diesel alike, fear and respect him. Despite his aggressiveness, he will help on occasion since Sir Topham Hatt brought him back, but only when it suits his personal interest. He has a caring side, but he very rarely shows it. He lives at the Dieselworks with many other diesels.
Diesel 10 is a BR Class 42 "Warship" with an added non-regulation hydraulic claw.