Cleo from Math StackExchange's Identity Has Been Revealed?
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The leading theory always _was_ that Cleo was some ex-soviet guy well-versed with symbolic integrals trolling around a bit. The fact that it's been revealed doesn't make it any less great, in fact it cements it as one of the greatest mathematical trolls.
The related video is absolutely worth a watch by the way, the motivation behind the trolling is brilliant. It's not that he explicitly set out to troll people, but that it was the only way to coax people into proving conjectures that he had. True to the theories, his hobby was literally just solving complicated integrals and this was the only way he could get people to join in on it. Knowing this makes the Cleo lore even sweeter.
(Oh, and the other bombshell is that for the particular infamous problem, Cleo actually did have a solution worked out, but V. just wanted to see how other people approached it)
Vladimir Reshetnikov