Bill and Ben are two cheeky twin engines who work privately at the Sodor China Clay Company, at the South end of Edward's Branch Line.
Bill and Ben are Sodor's mischievous saddle tank engine twins, who have great fun in teasing the other engines of the railway. They live and work at the China Claypits with BoCo, Timothy, and Marion. Their loads of clay can be used for many things such as paper, paint, and pottery. They take trucks for engines on the main line and ships in the harbour and are regularly seen around Brendam Docks. They enjoy attention and love taking visitors and being photographed. They tend to work together, like most twins, but even this youthful pair can have their arguments among themselves and can squabble with one another. They are highly prone to playing tricks and being cheeky. They usually like to tease Thomas, Edward, BoCo, and Timothy because they are the only engines who can really keep them in order. There is no real harm to them, but even Edward admits that they are maddening at times.
Bill and Ben are based on the Bagnall 0-4-0STs "Alfred" and "Judy" of Par, Cornwall, who are both preserved and in working order at the Bodmin and Wenford Railway.