For me, it would be GLaDOS.
Portal 2 spoiler
She deleted the one remaining human part of herself because it was just too much to deal with. She releases you at the end of Portal 2 as a path of least resistance measure because “killing you is hard.”
What about you, what is your favorite media villain?
Hmm, a rather difficult question, I have quite a lot of them and I could not get attached to any of them, well, maybe him:
and him: