Douglas and his brother Donald are twins. Sir Topham Hatt had only ordered one goods engine, but when both Donald and Douglas showed up he decided to keep them both. Donald and Douglas love to play practical jokes, especially impersonating one another. They were fitted with nameplates to specifically end this element of their humour.
Douglas is the #10 engine. Douglas is a 0-6-0 tender engine based on the 812 class built for the Caledonian railway.