Movies with a menacing female villain?

Imagine Darth Vader but female. Someone who is complex, has a (or is twisted by) darkness, can be ruthless and will murder hundreds without batting an eye. I'm looking for that level of menacing. It doesn't have to be sci fi or a fantasy setting as long as she retains the traits of being menacing and willing to kill innocent people. The more stoic and complex she is, the better. Thanks! :)