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?
I really love Killgrave as portrayed by David Tennant in season 1 of Jessica Jones. A completely amoral hedonist with the power of absolute mind control over anyone he speaks to. He is absolutely terrifying.