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?
the swarm from stanisław lems “invincible” (not the invincible show, this is a completly unrelated sci fi novel) (also the swarm is not really a villian its more like defending its territory