Which engine is known as 'the really useful engine'?

The engine known as “the really useful engine” is Thomas.

Thomas is the central character of The Railway Series, the children’s books created by the Rev. W. Awdry. He first appeared in the 1946 book Thomas the Tank Engine, which followed the debut of the wider series in 1945. His familiar slogan reflects the railway’s ideal that an engine should be dependable, hardworking and ready to take on different jobs.

In the stories, Thomas works on the fictional Island of Sodor under Sir Topham Hatt, traditionally called the Fat Controller in the British version. Although Thomas begins as a small tank engine and station pilot, he eventually handles passenger services and other duties, proving his usefulness through practical work rather than sheer size or power.

A common mix-up is Gordon, who is the railway’s express engine and one of its strongest locomotives. Percy, Edward and Gordon are all useful engines too, but “the really useful engine” is Thomas’s defining title and catchphrase.