Angel (season 1)
At the end of the third season of "Buffy", the 242-year-old, re-ensouled vampire Angel left Sunnydale to give teenage Slayer Buffy Summers the chance to live a normal life. Angel is now living in the big city of Los Angeles. With Buffy gone Angel is now completely cut off from society, every day getting closer and closer to giving in to his vampiric hunger. It's not until he befriends the half demon and fellow Irishman Doyle, who is sent visions of people in trouble by The Powers That Be, and fellow Sunnydale resident Cordelia Chase, who grounds Angel's life in the humanity around him, that he truly begins to take charge of his life and seek atonement for his past sins. He sets up his own detective agency, Angel Investigations and begins to "help the helpless".
Buffy the Vampire Slayer Season Eight
In the series' penultimate arc, Twilight is revealed to be Buffy's former lover, Angel. Angel attempts to explain that his Twilight persona was used to unify the anti-Slayer movement, thus limiting the potential destruction they could have caused working independently. His secondary goal was to push Buffy's development so that the two of them could reunite romantically and ascend to a higher plane of existence, itself called Twilight. However, whatever magical effect Angel was under seemed to wane after Buffy realised she was needed back on Earth to assist her friends as demons poured in from other dimensions to destroy the old universe. At the last moment, Buffy's other love, Spike, arrives in a futuristic ship to announce he has a solution to the problem at hand. In the final arc, "Last Gleaming", Spike's information leads them to the source both of magic and of Twilight's power, a mystical "seed" buried beneath Sunnydale. Giles plans to destroy it, but Twilight possesses Angel and compels him to kill Giles by snapping his neck. Distraught, Buffy smashes the seed herself. Twilight is stopped but magic is also removed from the universe. Though Slayers and vampires retain their powers, witches for example are left entirely powerless. Subsequently, Willow breaks up with Kennedy and Faith inherits Giles' estate and attempts to begin Angel's rehabilitation. A pariah in the community of Slayers and former witches, Buffy moves to San Francisco where she lives as a houseguest at Dawn and Xander's apartment, and resumes her former duties as Slayer: patrolling at night for vampires.