Daniel Mousetrousers
Daniel Mousetrousers was the thief behind the "Great Drain Robbery". Convinced that the manhole covers of Ankh-Morpork were made entirely of gold, he stole several dozen. Some of the less observant of the citizenry lost their lives as a result.
As a lesser result, any unprofitable theft is now known as "Doing a Mousetrousers".
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See also the real life phenomenon of manhole cover theft.