Ganondorf was defeated by a diminutive Robin Hood-wannabe in tights. Palpatine was defeated by his own lieutenant and his farm-boy son. Sauron was defeated by Bilbo Baggins. I don't know who Arthus or the Overlord were defeated by, but going by the other three, it was probably pretty embarrassing for them both.
The only possible choice IMO is Big Brother. "He's" the only one of the entire list who succeeded in everything he did. Partly, of course, because there was no Big Brother - just a succession of greedy bureaucrats using the cover of fake socialism to screw everyone over for their own benefit. Not entirely unlike the modern day British Labour Party (also advocates of universal surveillance, except when it comes to their own wage packets). And that comparison was FAR too easy to make.
