The Fat Controller (more formally referred to as Sir Topham Hatt), is the head of the railway in The Railway Series of books written by the Rev. W.V. Awdry. In the first two books in the series (The Three Railway Engines and Thomas the Tank Engine) he is known as The Fat Director. In the third book (James the Red Engine) he becomes The Fat Controller, as the railway has been nationalized. His full name is revealed in the foreword to the book Henry the Green Engine.
The Fat Controller also appears in many episodes of the television series Thomas and Friends, adapted from the books. In this he was usually portrayed in the form of a static figure, but from Season 12 onwards was portrayed using CGI.
The name or term "fat controller" has since been adopted in various contexts in the English language, beyond the sphere of the original stories.