Game: System Shock 2
What Makes Her Bad: She's a supercomputer gone rampant with a disdain for humanity.
What Makes Her Cool: That bizarre, fragmented voice, eerie portraiture, and manipulatory tactics? Hnnnng.

What was more chilling in System Shock 2 than the revelation that everyone you thought was still alive had actually been annihilated, and all you had done aboard Citadel was secretly being manipulated by the maniacal SHODAN? Look at you, hacker. You're no match for this eerily intelligent supercomputer with delusions of grandeur.