Angel
We originally saw Angel when he appeared on Buffy, He was her knight in shining armour. He help her countless times with both information and his immortal strength.
The one time he had to turn for someone else to help was when Buffy was killed by the master and being a vampire he couldn't bring Buffy back to life, he needed the help of Xander, the one person that had never liked him.
He left Sunnydale after assisting Buffy in killing the Mayor, that night was to be the last he ever saw of his one true love. They both knew they could never be together, but they also couldn't be apart and still see each other.
Angel moved to L.A where he continued to rid the world of his kind. that's where he met up with Doyle, who was sent to help him by the powers that be, he then met up with Cordelia who he knew from Sunnydale.
Together they formed Angel Investigations helping those in need, but for a price!
Angel continued to think about Buffy, making him seem broody.
Doyle eventually gave his life to save Angel from sacrificing his.
Along came Wesley, faith's old watcher claiming to be a rogue demon hunter. enlisting angels help to find a very nasty demon he had been hunting
Angel also met Gunn who also hunted and killed vampires. he became part of Angel investigations
When Wolfram and Hart brought back Darla his sire he became distant from his friends, there was more history between the two vampires than anyone could comprehend. Angel and Darla became close again. But when Wolfam and Hart brought Darla back she was human, Angel tried to keep her on the right path, but she was dying, but still he continued to try to keep her from becoming what he feared the most for her, a vampire! his struggle was not to be, Wofram and Hart brought Drusilla back to turn Darla. Angel watched as Dru sunk her teeth into Darla's neck, unable to do anything but watch.
Into the 3rd series of Angel Darla returns, pregnant with Angels child!
Angel is happy to kill Darla until he finds the child inside her has a soul. the question still burns, how? a vampire cannot father a child!