Fred is a diesel working on the Skarloey Railway.
The Skarloey Railway bought two worn out Hunslet diesels from the National Coal Board and, using parts from both engines, constructed Fred. He was put into service in 1989 as a secondary diesel, and is used mainly for maintenance and engineering work, with a maximum speed of 9MPH and used exclusively for engineering work on the Railway.
Fred made his first appearance in the book New Little Engine, but was only mentioned briefly when he wouldn't take a weedkiller train!
It is assumed Fred is lazy and tries to stay out of work by pretending to be ill.