David Boreanaz played Angel, whom Buffy met in the first episode of Season 1. At first, she does not know who he is — Angel merely gives her a cross, warns her about some upcoming “harvest,” and adds that he wants to kill the vampires but is afraid to try. Later, we learn that he is a vampire who is more than two hundred years old and was cursed by gypsies after his last kill. The curse restored his soul (though he is still a vampire), and now he is tormented by the memories of his victims. He and Buffy date (somewhat off and on) and fight evil for three years. Angel leaves at the end of Season 3 (for his own show), though he makes guest appearances later on.
James Marsters portrayed Spike, who first appeared in the third episode of Season 2. He was a nerdy, British aristocrat who wrote bad poetry and was a laughingstock of both men and women. After Druscilla turned him into a vampire, he turned into a “bad boy,” killed two slayers, and dated his sire. He brought Druscilla to Sunnydale, tried to kill Buffy, and eventually joined forces with the slayer against Angelus. Later, the government neutered his ability to harm humans, and he eventually joins the Scoobies, dates Buffy, regains his soul, and dies saving the world at the end of the series (though he later joins Angel in Los Angeles).
Julie Benz was Darla, who sires and then dates Angel in Ireland, joins the Master in Sunnydale, and tries to get Buffy to kill Angel (who had since changed “teams”). She is the first vampire we see in the first episode of the program, and she is later killed by Buffy in the first season. Darla is later resurrected in the “Angel” spin-off series. In that program, she comes back as a human and is then turned into a vampire again by Drusilla. Later, Dara and Angel have a son, Connor, during whose birth Darla stakes herself and who plays a significant role in the last two seasons of “Angel.”
Juliet Landau portrayed Drusilla, a holy woman in England who sees visions and with whom the vampire Angel becomes obsessed. He kills her family, drives her insane, and then turns into a vampire just before she takes her vows to become a nun. She begins dating Spike, who takes her to Sunnydale to restore her health after a mob attack in Europe. Later, evil Angel (Angelus) joins forces with her in Season 2 to try to destroy the world. Spike and Druscilla leave Sunnydale at the end of the season, and she later dumps him and then appears in the “Angel” spin-off.
Mercedes McNab played Harmony Kendall, a ditzy, superficial friend of Cordelia who is turned into a vampire during the battle between Sunnydale High’s students and the Mayor at the end of Season 3. She starts to date Spike after Druscilla dumps him and appears in Seasons 4 and 5 until Spike realizes that he loves Buffy. Later, she joins Angel in the last season of the spin-off series. She starts out as someone in the secretary pool of Wolfram & Art and is then promoted to being Angel’s personal secretary after he and the other protagonists take control of the Los Angeles branch of the firm.
Mark Metcalf was The Master, a centuries-old “vampire king” of Sunnydale (if not much of the western United States). He had been trapped by a force-field in a destroyed, underground church during a long-ago earthquake, and he needs the “harvest” (described in the first two episodes of Season 1) to be released, walk the earth, and unleash a literal hell. After a season of battle and (temporarily) killing Buffy in the last episode of the season, he is killed by the slayer. The Master makes a brief appearances later in the first episodes of Season 2 (in Buffy’s post-death dream) and Season 7 (as a guise of The First).
Other “Buffy” Demons and Enemies
Emma Caulfield portrayed Anya Jenkins, a Swedish woman who became a vengeance demon centuries ago after cursing her husband for his unfaithfulness. She appears in Season 3 after Cordelia breaks up with Xander, hoping that she will be able to curse him on Cordelia’s behalf. Anya becomes human again after her spell is broken. Anya goes out with Xander in Seasons 4 and 5, and the two later become engaged. After Xander breaks up with her right before the alter in Season 6, Anya becomes a demon again (though only for a little bit). Anya , after finally understanding humanity, dies in the final episode of Season 7.
Adam Busch played Warren Mears, a women-hating geek who builds robot women (for himself and Spike) in Season 5, turns evil in Season 6, and accidentally kills two real women before being killed himself by Willow in revenge for the death of her girlfriend Tara.
Nathan Fillion was Caleb, a former Roman Catholic priest who becomes a servant of The First Evil in Season 7. He kills potential slayers, severely wounds Xander in a permanent way, mocks Buffy because she is a woman, and is later killed by her.
Harry Groener portrayed Mayor Richard Wilkins III, a centuries-old human who owes his immortality and success to all of the tributes to various demons he makes. In Season 3, he decides to “ascend” to become a pure demon — an action that will involve the eating of the graduating class during the graduation ceremony. Buffy kills him in demon form in a particularly-explosive fashion.
George Hertzberg played Adam, a “thing” that was made by the Initiative — a secret, government, demon-fighting operation — that first appears in Season 4. He is one-third demon, one-third human, and one-third machine. He kills demons and humans to learn more about each, and then creates a plan for even more carnage.
The First is the ultimate, incorporeal evil that manipulates humans, vampires, and demons into doing its bidding. It cannot make physical contact, so it relies on psychological warfare while being able to take the form of anything that is deceased or had been once dead. It appears once in Season 3 and is the Big bad of Season 7.
Clare Kramer was Glory, a hell-god who fell from her hell dimension and was unable to return to her “home.” To do so, she needs to find a “key” that will bridge the gap between the earthly and demon realms — but destroy the world in the process. The “key” turns out to be Buffy’s (new) little-sister, and Buffy saves the day by making the ultimate sacrifice in Season 5.
James Leary as Clem, a friendly demon in Season 6 who is protective towards Dawn, helps the Scoobies, and enjoys playing poker (though for little kittens).
Tom Lenk portrayed Andrew Wells, a dorky guy who joins Warren and Jonathan in their evil schemes in Season 6. He may or may not be gay, and he seems to like Warren a little too much — an action that causes him to kill Jonathan in Season 7. Later, he atones for his crimes and joins Buffy and her friends in the fight against the First Evil that year (and afterwards).
Kali Rocha played Cecily/Halfrek — Anya’s vengeance-demon friend over many centuries, who is later killed by their boss after Anya tries to escape becoming a demon for the second time.
Danny Strong was Jonathan Levinson, who randomly appears in Seasons 2 and 3 as the butt of the jokes of the popular people in high school. He tries to kill himself in the clock tower of Sunnydale High in Season 3, casts a spell in Season 4 to make him popular, and eventually joins Warren and Jonathan in Season 6. He is killed by Andrew in Season 7.