Diesel 10 is an evil diesel engine with a semi-sentient, hydraulic claw, which he has named "Pinchy"
Diesel 10 is an evil, conniving, manipulative, bullying and raving diesel engine. He absolutely despises steam engines, would call them taunting names like "Puffball" and "Teapot" and is not above doing anything to get rid of them if possible. He is Sodor's strongest (but not quite largest) diesel, his power being enforced by his slightly malfunctioning claw, Pinchy. He can use this deftly, and is even able to use it to make a sculpture. Pinchy, though, seems to have a mind of its own, as it has been shown to "punch" Diesel 10 in the face from time to time, which he loathes. All engines, steam and diesel alike, fear or respect him.
Despite his brutality, some of his demeanour appears to have cooled, and his behaviour has apparently improved enough that the Fat Controller allowed him back to the Island of Sodor. He gets along enough with the other Sudrian diesels, but his efforts to help are often only when it suits his personal interest and he still harbours his scheming ways and anti-steam sentiments.
Diesel 10 is based on a British Rail (BR) Class 42 diesel-hydraulic engine with an added non-regulation hydraulic claw. All but two members of the class were named after Royal Navy warships, so they, and the similar Class 43 (not to be confused with the InterCity 125 power cars with the same class number, the basis for Pip and Emma), were nicknamed "Warships". Two of these engines are preserved, D821 Greyhound and D832 Onslaught. It is possible that Diesel 10 was based on D832 Onslaught as ordered by British Railways before he had Pinchy installed.
In real life, adding in a hydraulic claw onto a diesel engine would most likely be considered illegal, if it was not approved by government authorities.