Angel was born a human in Galaway, Ireland. His human name was Liam but he hated work, and prefered to flirt with the ladies. He saw Darla, a vampire, when he got kicked out of a tavern for drunken behaviour and she sired him then. They were lovers, and together they terrorized and killed all over Europe for several centuries. Angelus, as Angel's sister named him, killed his family, his friends and everyone he knew.
One day Darla showed him Drucilla. She was a pure catholic school girl who had visions. Angelus first made her insane by killing her family and friends. But the day she came to take her vows as a nun at a convent, he turned her into a vampire. The three killed and maimed until Drucilla started to get bored. Angelus brought her Spike to sire.
Drucilla and Spike, Darla and Angelus went around Europe killing and eating. Spike drew attention to himself everywhere the group went so Angelus told him about the slayer. Spike killed two slayers, and after the first one, became a permanent couple with Drucilla.
Soon after that, Angel got cursed with a soul by a gypsy Romany tribe for eating a gypsy girl Darla brought him. All his guilt and sadness for the people he had killed and sired came back to him, and he spent the next hundred years or so hanging out and working on his brooding skills. He wanted to go back to Darla but she shunned him and Spike and Drucilla left. Angel went to New York, ate rats and couldn't see his place in life anymore. Whistler, a half-demon sent by the powers that be, brought Angel to the slayer who he fell in love with, and vowed to protect her.
Angel showed himself to Buffy the first day she moved to Sunnydale. The pair soon fell in love but everyone could see the relationship wouldn't last. In season 1 Angel showed Buffy his true identity when Darla, his sire framed Angel for attacking Buffy's mom. Angel staked Darla.
But it wasn't all hugs and puppies when Spike and Drucilla came to town, Spike intent on killing the slayer. When he couldn't do it himself, the pair tried to reassemble the Judge. Angel and Buffy found a part of the Judge and Angel prepared to take it to the other side of the world. But Spike's minions took the part, and Angel and Buffy went back to his apartment and connsumated their relationship. In doing so, they unwittingly turned Angel back into Angelus, the killer of Europe.
Angelus killed Miss Calendar, attacked Buffy's friends, and proceeded to flirt with Drucilla. Miss Calendar was a desendant of the gypsy tribe who cursed Angel with a soul years ago. She had been sent to Sunnydale to keep an eye on Angel and make sure he didn't lose his soul. He did, and he killed her while she was trying to curse him with a soul again.
Angelus joined up with Spike and Drucilla who had come to Sunnydale to bring about the end of the world. He started the ritual that would suck the world into hell, but meanwhile Willow had discovered the ritual that would curse him with a soul again. Angel started his ritual, and prepared to bring about the end of the world. Willows ritual succeded, but Buffy still had to kill Angel to stop the end of the world. Angel went to hell.
In season 3, Buffy lets go of Angel's memory by leaving her claddagh ring that Angel gave her in his warehouse. Then comes the ultimate- Angel is back! He had suffered centuries of torture, but still gained some resemblence of his human form.
Angel doesn't know why he is back, and a demon haunts him in the shape of his former victims. Angel decides to kill himself by waiting outside for the sunrise. Buffy tries to stop him, but the thing which does, is snow in Sunnydale.
Angel now realizes he has a purpose in life. He decides to leave Buffy and Sunnydale for L.A. after the dealings with the mayor. He breaks up with Buffy and she is heartbroken but she decides to go to the prom anyway. Angel shows up for the last dance.
Only Faith stabs him with a poisoned arrow which only a slayer's blood can cure. Buffy stabs Faith, but Faith falls onto the back of a passing lorry. Buffy forces Angel to drink from her, but she survives to fight the mayor, and Angel leaves for L.A. But that's not the end of Angel's story...