Films: Probably Scorpio from Dirty Harry, Andy Robinson plays this psychopath really well, you really have to see the movie to get what I mean, but this is a guy who pays a thug to beat him half to death just so he can frame Clint Eastwood to get him off his back so he can resume his killing spree. Plus that part with the kids on the school bus was really disturbing, chilling stuff. The part was played so well that Andy recalls receiving several death threats in real life because people were that disturbed by his performance (stupid of them, but still he was SO good that it almost ruined his career.)
I liked Ed harris as Major Konig: the German sniper from Enemy at the gates. He was quite menacing and his cunning was
pretty good at showing his ruthless pragmatism. E.g. using dead bodies from his own side as decoys or hanging Sasha and using his corpse as bait to try and egg Vasily on into exposing himself. I thought this really pinned him down as a memorable antagonist who really made the movie for me.
Games: I liked Dutch Van der Linde from Read Dead Redemption quite a lot, his banter dialogue in the Blackwater missions were pretty well done, plus the foreshadowing he gives just before his death on the cliff top about the Bureau finding another monster was memorable, his in general craziness mixed with his charisma made him likeable yet despicable as a character and hard to forget. Ross was brilliant too, his dialogue was done very well and gave the player a good view into how ruthless he could be as a villain, a lying, cheating, government type who really knows how to settle the score with those he deems outside the law, of course his "everyone pays for what they've done" comes back to bite him when Jack gets his revenge a few years later, I really enjoyed the ironic twist there, good stuff.
One of my other favourite bad guys, is Fulgrim from the Warhammer 40'000 universe, Primarch of the Emperors children chapter. He and his start out as a personification the Imperial creed and seek to emulate the Emperors perfection in every way only to fall into a bottomless well of depravity and psychotic self-indulgence thanks to the Heresy and the chaos god Slaanesh. His downfall was really interesting to read about in the Black Library novels, the moments of remorse he shows after slaying Ferrus Mannus made him more human than a lot of other Primarchs and also there's the fact that during and after his corruption he manages to kill an unrivaled two other Primarchs, which is badass achievement in itself. I think out of all the space marine legions and Primarchs, Fulgrim and the third legion have the best appearance, I love the purple/gold white hair combo. Swore to myself that I'd put together a pre-heresy Emperors Children army one day after reading about them, haven't got round to it yet though sadly.