Who’s your fat friend, Thomas?

The other day one of my (grown-up) daughters queried the way I said Fat Controller and not Fat Controller (I cannot remember how the subject came up). When I explained, she confessed that throughout her years of devotion to Thomas the Tank Engine in the seventies she had always thought his title meant that he was some kind of dietician, though she could not say why she had imagined expertise of this kind was relevant to the operation of a railway.

Wikipedia has masses of stuff about these feebly anthropomorphic but hugely popular stories which have given rise to a world-wide marketing phenomenon:
The name Fat Controller has been the subject of much controversy because of the supposed political incorrectness of the name. In America in 1989 the ACLU successfully argued that censorship of this name would violate the First Amendment to the United States Constitution. Nonetheless, the nickname has been downplayed in recent years in favour of Sir Topham Hatt. The name is always used with affection in the books and the television series—the adjective "fat" being simply a description. [The railway where the stories are set] also has a Thin Controller and a Small Controller.
The Fat Controller has proven to be a popular figure outside of the world of Thomas. In British slang, the name has come to symbolise any authority figure linked with transportation. The most notable figure of recent years to be compared to Sir Topham is the British Deputy Prime Minister, John Prescott. A rather more contemptuous term, "fat cat controller", has been applied to the executives of transport firms.