Thomas the Tank Engine is the number one engine on the Island of Sodor. He is a fussy little blue engine with red lining, six small wheels, a short stumpy funnel, a short stumpy boiler and a short stumpy dome. Thomas is very cheeky and over eager at doing things more suitable for much bigger engines. As a result, Thomas often gets into different kinds of trouble, which can make him very upset. Luckily, Thomas never feels the blue for a long time, and soon he starts huffing and puffing again along his Ffarquhar branch line on the North Western Railway. Thomas works with his two coaches Annie and Clarabel, and sometimes gets help from Percy and Toby. He likes to work hard and always strives to be a Really Useful Engine on the Island of Sodor. The Fat Controller, Sir Topham Hatt, is very proud of Thomas. Thomas was awarded his own branch line after he rescued James.
The design of Thomas is based on the London Brighton and South Coast Railway 0-6-0 E2 with extended side tanks.