Angel's Life

Angel started life as Liam, a shiftless Irish drunkard in his 20s. He was turned into a vampire by Darla, in an alley outside a bar. He took the name "Angelus" and almost immediately killed his entire family. He and Darla then terrorized Europe for over a hundred years. It seems that they enjoyed a sexual relationship, although their primary lust was for human blood.
His restoration to goodness began when Darla brought him a gypsy girl for a birthday present, whom he tortured and killed. Her father, in revenge, cursed Angel by restoring his soul. Angel became a being tortured by his conscience; he was not a true vampire, because he was unable to kill humans, but neither was he human.
After a hundred anguished years, a demon named Whistler showed Angel a high school sophomore named Buffy Summers, who was marked as the next "Slayer". Angel found a purpose in helping Buffy. They fell in love and, on her 17th birthday, consummated their relationship.
The perfect happiness of loving Buffy had the unexpected side-effect of lifting the "curse", and Angel lost his soul, becoming once again the evil Angelus. His soul was eventually restored, but he could not bear to be around Buffy, as he was unable to love her. He thus went to Los Angeles -- the "City of Angels" -- to seek his destiny.