What’s the origin of the phrase ‘Mutt and Jeff’?
The Mutt ‘n’ Jeff variant is is a nice example of Cockney rhyming slang. It originated with that meaning in the UK in the 1960s and is sometimes shortened just to ‘mutton’. Both forms of the phrase derive from Mutt and Jeff - characters in a comic strip created by Bud Fisher in 1907.
The other meanings that relate to variable size etc. allude to the fact that in the Mutt and Jeff cartoons one was tall and the other short. Fisher built a successful career from drawing the comic strip and he produced this cartoon of himself with Mutt and Jeff, captioned ‘The Three of Us’, in 1912.