Well, had I bothered to look it up first, I would have found out that muller means 'a heavy smooth object made of stone, metal, wood or glass, used for grinding paints or drugs on a flat surface' - so now I know! Unless there was someone called Muller ......
At the risk of being taken away by the men in white coats for talking to myself, there was of course Gerd Muller, the German footballer, and also Egon Muller, the speedway rider. Don' think this phrase refers to either of them though.
According to http://www.worldwidewords.org/qa/qa-mul1.htm
But I can remember my Dad saying "Moolahed"..Moolah being a slang term for money ..so this meant that having spent all their money on drink they were moolahed or drunk !
No doubt QM will be along to give a proper explanation !
Thanks for the confidence, Shaney, but I must confess that - just like Michael Quinion in your link - I have heard the word used only in the sense of 'drunk'. As it happens a 'muller' is...hardly surprisingly, perhaps...any vessel in which wine is mulled, so I suppose there could be an 'intoxicated' connection there.
I think lankeela's "heavy object for beating or grinding" stands up - it's obviously (dangerous word to use - ok, try "probably") related to "maul", which is a heavy mallet used by stonemasons, amongst others, and unsophisticated boxers are sometimes referred to as "maulers". (That's the fighters, not the dogs or the underwear!)
Incidentally, the surname "Muller", at least if it's Germanic, means "miller". It should be spelt "M�ller" (or "Mueller", as the umlaut in German denotes an omitted "e").