The Life, Death and Times of Angel
Angel, born as an Irish kid named Liam who used to get drunk, fight and rebel against his father, was sired (turned) in an alley by a prostitute-turned-vampire called Darla and became known as Angelus--the demon with the face of an angel. Together, they would cause terror, mayhem wherever they went and when others had a massage, they'd have themselves a massacre. One day, after killing a young gypsy woman, he was cursed with a soul which gave him a conscience that causes him eternal pain and suffering for all his horrific deeds. He stopped killing and feeding on humans. If Angel experiences just one moment of pure happiness, he loses his soul and turns back into Angelus.
Angel stumbled through the world, feeding on rats and living in the shadows for decades until he was given a purpose by a mysterious figure named Whistler. The man pointed him towards a certain Slayer (Buffy, duh!) whom he was supposed to help in her fight against the forces of darkness. They naturally ended up falling in love and since one thing usually leads to another, they made The Sex and unbeknownst to both of them, that qualified as a moment of pure happiness for Angel (being loved despite his horrible past by a Slayer of all people) and thus the bloody mayhem was on. When he tries to open a portal that would unleash hell upon earth, Buffy is forced to kill him, sending him to a hell dimension since his soul had been successfully restored but not until the portal had already been opened and only his death would close it.
Naturally, he managed to magically reappear--most likely his destiny had not been fulfilled--but he ended up leaving the little town of Sunnydale (as well as Buffy) behind to move to Los Angeles to once again live in solitude. Easier said than done, Angel soon found himself surrounded by a wacky, thrown together family of lost souls (some of them from Sunnydale) who would "help the helpless" under the banner of Angel Investigations. One day, he came across an old prophecy telling of a vampire with a soul who, once he redeems himself, would be granted life as a human once again. Angel had enough of brooding in the dark and set out on his path to redemption.
In the big city, suits have all the power so Angel's main-baddies came in the form of lawyers working for Wolfram & Hart, a law firm that not only represented evil, but had existed since the dawn of time in some form or another. Wolfram & Hart, however, didn't want to kill Angel, they wanted him to turn into Angelus again so he would play for their team. They went as far as to resurrect Darla with the idea being that she'd give him a moment of happiness which ultimately failed. In turn, their unique condition let them conceive a child, Connor, who was kidnapped by a reawakened former surviving victim of Angelus and raised to hate his father in a demon dimension where time passed faster than on Earth.
Many deaths and bad decisions later, Angel was presented an option to save Connor (as opposed to killing him) by taking over Wolfram & Hart and in turn erasing Connor's memories (along with everybody else's except for Angel) so he could live a normal life. Angel accepted, working with his team from within the belly of the beast, trying to avoid being corrupted. This, of course, had been another attempt by Wolfram & Hart to bring him over to the nasty side of good and evil. Angel slowly realized this and made a big play to take the fight to them. Ultimately, Angel found himself in another dark alley, with friends dead or dying, hordes of monster about to attack, picking up a sword and ready to fight.