Thirteen is a black saddletank engine from The Other Railway, who once had an open cab.
Thirteen was a spare engine from the Mainland and was brought to help Donald and Douglas, who were feeling overworked. When he first arrived, he proved to be very unlucky. He caused delays for Donald and Douglas, got hit by a land-slide, and then damaged his firebox which got knocked out of place. Sir Topham Hatt sent him to The Works, and Donald and Douglas thought that would be the end of him.
However, after his repairs he came back to Sodor with a bigger firebox and a proper cab which cured his unluckiness. He told Donald and Douglas that he came to Sodor as an unlucky engine, but returned to the Mainland as a very lucky one.