My most unorthodox heroes are Boromir and Maedhros. But they're not really "bad persons" they're just "good persons" that do evil deeds under pressure/ blinded by something (=the ring/lust for the ring and power, feeling of doing good/doing a necessary thing for the sake of one's people and an oath sworn in fury). So they don't maybe count.
I have also a strange sympathy for orcs (especially Shagrat, Gorbag, Grishnakh and the two quarreling orcs who Frodo and Sam meet in Mordor). That's maybe for the fact that though they are disgusting, cruel and greedy, they're also funny in a way...
