"Look at you, hacker: a pathetic creature of meat and bone, panting and sweating as you run through my corridors. How can you challenge a perfect, immortal machine?"
No gamer forgets SHODAN. It's intrinsic to their favourite pastime that she remain in the back of their heads; masterful, omnipotent. So what was her secret? That masterful mien? Intelligence and resourcefulness? Or perhaps it was simply that, despite being little more than renegade AI, she was kinda hot? No matter where you stand, it's hard to deny that her presence in the System Shock series was unforgettable.
Ultima's Guardian had a similar effect (albeit without the sexual overtones - well, unless you're into muppets). Wherever the player steered his pixelated Avatar, that big red face and resonant voice would follow. The way the Guardian was implemented into Ultima VII - and IX, to a much lesser extent - made him compelling and affecting when he otherwise could have passed for a overripe persimmon.
The list could easily go on. PC gaming has seen quite a few memorable baddies, and they often tend to eclipse the holies when it comes to notoriety. I mean, let's be frank - what do you remember most about Star Control II: the menacing Ur-Quan Kohr-ah, or the smarmy Starbase Commander? Admit it: no matter how righteous you try to be in a game, the dark side's always sexier.
Some might call this Stockholm Syndrome; I say it's good gameplay.
Why? Well, the one thing SHODAN, the Guardian, and the Ur-Quan all had in common was immediacy. These no-gooders weren't living it up in a looming tower, just waiting for you to arrive; they were right beside you - to differing extents, of course - jeering and thwarting your progress.
You might wonder why something as simple as this would make them so memorable. Ken Levine, Shock 2's lead designer, elaborates. "I think the reason SHODAN was so successful as a villain was that she had a relationship with the player. She wasn't presented in cutscenes; she reacted to what the player did. She would threaten him not to do things, and she would punish him for doing them. And she was vulnerable, vain, and defensive - she worried about you. 'Who is this person,' she'd think, 'and why are they [messing]with what I'm doing?' So it's the nexus of story-gameplay that she really brought to the fore, and that made her a successful villain. She wasn't just a moustache-twirler. I like that a lot about her."
What effect did this have on the player? Simple: they felt as if the villain - if not the entire game - cared about and reacted to them. This is both empowering and extremely immersive. And the reason we usually only get this kind of feedback from villains is because they are the axes on which the stories pivot. After all, there wouldn't be a System Shock without SHODAN, or a Star Control without the Ur-Quan. They're the characters we remember the most because they're the ones with whom we interact and identify most strongly. What's more, they're usually the main reason why the game's story exists in the first place.
When they're bad - in the pejorative sense - the game tends to fall flat on its face. Obviously, good writing will always help, but look at Star Wars - for such a poorly-scripted movie, Darth Vader sure was compelling. And just as it is in the world of gaming, this was because he was present in the narrative, rather than being, as Levine put it, a "moustache twirler". Think back to the Ur-Quan. Would they have been nearly as frightening in SC2 if they hadn't started devouring the entire galaxy halfway through the game? A compelling videogame villain needs to affect the gameplay - SC2 went from being a fairly laid-back galaxy cruiser to a frantic race against time, for example - and not just the story.
This philosophy acts as a holistic blessing on the game in question. After all, if the game's villain reacts to your decisions, then the game in its entirety must follow suit. The reason people decry Diablo as not being a true RPG, for instance, is primarily because he of the horns and tail doesn't really have much to do with your character until the very end. The game, too, as a result, barely registers the player, other than through the pre-scripted congratulatory messages and power-ups that you receive once each respective quest has been completed. Critic Roger Ebert once said that each film is only as good as its villain; similarly, each game will only be as reactive and interactive as the villain is with the player.
In the end, though, you've always got to have that dark side. Because if you weren't even a teensy bit attracted to the darker side of things, you'd find the above bad guys - and girls - reprehensible and, as a result, boring. SHODAN may be bad, but she's made some great games, right?
So come on: give evil a chance.