Cole is half demon, half mortal. His demon name is Balthezar. one of the most powerfull demon that the world has ever seen. He was sent by the tryad to kill The Charmed Ones, but winds up falling in love with Phoebe while he is disguised as a DA. He has made many attempts to kill the sisters but then when he finally has the chance to kill Phoebe, he realized that he was unable to. Then he kills The Triad to save the sisters, thus successfully made the underworld to label him as "traitor". A bounty hunter, Krell, The Zotar, was then sent to go after him. In Sleuthing With The Enemy, Phoebe and Cole come to an understanding and Phoebe fakes his death after they vanquished the bounty hunter. Piper and Prue think he is dead but Phoebe knows he is alive and wants to see him again. However, as the plot in season 4 thickens, Phoebe and her sisters realized that Cole was, in fact, The New Source. Under such circumstances, Phoebe had no choice but to vanquish him. Although the love between them was strong, it was clear that The Source is controlling Phoebes love for Cole to make her pregnant, which might eventually become the most powerful magical being anyone has ever known, but sadly, planted with the seed of evil. Although the remaining sisters were quick to persecute Cole, Phoebe knows that deep down, Cole has never gave up trying to be good. But her duty as a Charmed One and his identity as The Source made it difficult for both of them to continue their love. Cole was vanquished for good in the middel of season 5.