THE GRAY HATS

Spike (James Marsters)
At first, it seemed that Spike would be the last vamp to go from "very bad man" to "sort of bad man" on the Evil-O-Meter. He rolled right over Sunnydale, literally, when he drove his old DeSoto through the "Welcome to Sunnydale" sign as he first arrived in town. And that wasn't by any means the limit of his destructive streak: the vampire formerly known as "William the Bloody" was a man with a mission, and that mission was to restore his crazy girlfriend, Drusilla, to her full power. Constantly trying to kill Buffy was just a fun perk. The games didn't last long, though; Buffy gained the upper hand and crippled Spike. Though he survived the encounter, he ended up in a wheelchair, and when an newly un-souled Angelus breezed back into the vampire high life, Spike wasn't happy with his reduction in power: he plotted with Buffy to send Angel to Hell, then blew town. He later returned to team with Buffy again when a cured Drusilla dumped his ass, then left town again to get his girl back. Finally, still unable to win Drusilla back, he returned to Sunnydale, where he was caught by The Initiative and implanted with a chip that prevents him from harming living things, and he suddenly found himself dependent on Buffy and her friends for protection, first from the Initiative, then from other demons angry about his alliances with the Slayer. He can't kill but is still evil, and he can't help but aid the Slayerettes, giving him just enough good to put him in the gray.
Current status: Still defanged and attempting to plot the Slayer's downfall and keep her from dusting his ass at the same time. We'll see how that works out for him.

Faith (Eliza Dushku)
You know that whole "one girl in all the world" thing in the slayer lore? That's just another rule that Buffy broke, and as a result of her death (even though she was only dead for a minute or two), another slayer was called. That one was killed by Drusilla, which resulted in Faith being called to serve. Unfortunately for Sunnydale at large, and her Watchers in particular, Faith was not the model slayer: after the death of her first Watcher and the betrayal of her second, she became a little harder than she had already been, and by the time Giles and Wesley got a crack at her, it was pretty much too late. When she accidentally staked a human man, Faith's true slide into darkness began, and she allied herself with the Mayor, who also happened to be the local evil. Under his employ, Faith became a fairly skilled assassin until she went after the wrong guy. When Faith shot Angel with a poisoned arrow intended to kill him, Buffy decided not to play Ms. Nice Slayer anymore and went after her former comrade-in-arms. Their battle ended with a wounded Faith taking a fall from a roof, but she survived the encounter only to end up in a coma. After waking to wreak a little more havoc, she traveled to L.A. where she got into a lot more trouble, but eventually found redemption with help from Angel, who's something of an expert on the subject.
Current status: Serving hard time after turning herself in to police for the crimes she'd been running from.

The Initiative
Their sort-of-good intentions kept The Initiative at large from being classified as a force of evil, but their methods and attitudes land them in moral ambiguity. The mission of this US government-funded military operation was a study and capture-and-release program for Hostile Sub-Terrestrials -- known to you and me as vampires, demons, and other things that go bump in the night. Initiative soldiers would stun and capture whatever creatures they happened across, then implant some of them, like Spike, with neural chips which prevent them from harming living things but allow them to beat on other demons. Not a bad plan, and pretty well-organized, too, with a bunch of hotties running around in military garb. Unfortunately their slightly deranged leader, Maggie Walsh, had even bigger plans, and created a Frankenstein's monster that ended up kicking Initiative ass. After a very big, very messy, and very costly final battle between Initiative soldiers and the creatures they'd been keeping in containment, the installation was left in ruins and the Initiative was no more.
Current status: Disbanded and dismantled, deemed a failed project by the US government.

THE BLACK HATS

The Master (Mark Metcalf)
A vampire so old he got really ugly, the Master had one major flaw as an ominous villain: he couldn't do any of the dirty work himself. Though he'd once reigned supreme as Mr. Evil Universe, an ill-timed earthquake trapped him underground in the remains of a church. Stuck behind a mystical barrier, he could do little but send various minions to see to Buffy's doom while plotting new evil with his Vamp Boy sidekick, The Anointed One. But as the old saying goes, if you want something done, do it yourself; the Master learned that the hard way when his underlings failed to kill Buffy. He eventually did kill Buffy himself when she ventured into his lair, but it just didn't take (death wasn't her thing, and it didn't do much for her hair, either), and she ended up kicking his ass and staking him with a well-placed broken support beam. He was nearly restored by his faithful minions, but Buffy put a stop to that, too, grinding his bones to dust with a big ol' sledgehammer.
Current status: Very, very dead.

Drusilla (Juliet Landau)
If you look up "crazy" in the dictionary... well, it'll just give you a definition of the word, but you'll find that that definition suits our girl Drusilla perfectly. Once upon a time she was a good, religious girl who received frightening mental premonitions that made her fear she was possessed; soon, she was, quite literally. An unfortunate encounter with Angelus led to the evil vampire forming an obsession with sweet Drusilla, and he drove her completely mad before turning her into a vampire. At some point after joining the blood-sucking family, Drusilla hooked up with Spike, and they terrorized Europe together, completely in love in that "let's go kill a bunch of puppies together" kind of way. But an attack by an angry mob in Prague left her weak and near death, so she traveled with Spike to Sunnydale in the hopes that the power of the Hellmouth, with the aid of a little magic, would bring her to her full strength again. They succeeded, but then Spike ended up weakened, and Drusilla found herself in stronger company with the return of Angelus. After Spike's alliance with Buffy, she decided her man had gone soft and took off to have tryst after tryst with various slimey demon types.
Current status: Last we heard, she'd dumped Spike again, this time for a fungus demon, and is probably off somewhere living the demon high life.

Mayor Wilkins (Harry Groener)
The Mayor was the Ward Cleaver of Super-villains. Though he was planning on turning into a giant snake-demon and eating everyone at Sunnydale High's Class of '99 graduation ceremony, he was awful polite about it, and he didn't tolerate cussing. The conflicting natures made him an interesting puzzle, but it just couldn't stand that the town Mayor was having people killed willy-nilly, so it was Buffy's job to put a stop to his plans. He had his own slayer, though, and Faith was something of a daughter to Mayor Wilkins; he stopped playing Mr. Nice Evil Man when Buffy put Faith in a coma. But even with a lot of anger on his side and his transformation into a giant serpent, he couldn't best the Scooby Gang, and Buffy and pals blew him sky-high, along with the high school. He did leave his legacy for Faith, in the form of a nifty body-switching device, leaving one and all to ponder how someone so evil could care so much, and he left his mark on Sunnydale as the only Mayor in town history to try to devour a large segment of the populace. Well, at least we hope he was the only one.
Current status: Blown into chunky snake-bits.

Adam (George Hertzberg)
What do you get if you cross a demon, a human, a blender and a set of Ginsu knives? You get something rather like Adam, complete with dastardly evil probably contributed by a Windows operating system. This modern Frankenstein's monster, created by Maggie Walsh and The Initiative, decided that he'd rather not be the perfect little science project he was intended to be, and after killing his creator, set off into the world to study the local human and demon populations through dissection. After that, his plans were for domination and zombification; after messing a bit more with the Initiative and showing off the floppy-eating disk drive mounted in his chest, he set about scheming to kill Buffy and bring down the Initiative. A strategic alliance with Spike, whose V-chip Adam promised to remove for services rendered, nearly delivered victory into his hands, but his plans crumbled, and Buffy got in touch with her primeval power to kicked his ass ten ways from Sunday.
Current status: This cyborinator bore the full brunt of Buffy's wrath; he'd be snake food, except that she killed all the snake-guys in town, too.