Cole is a powerful half mortal / half demon. Cole is his mortal side, and Belthazor is his demon half. Belthazor is a very powerful demon that was sent by the source to kill the Charmed Ones. Unfortuantly for that side, his mortal side Cole fell in love with one of the Charmed Ones, Phoebe. When he had to act like he was going to kill her, she returned the favor in order to save him from the source and her sisters, so she faked his death. He stayed away for a while, but soon he came back and told her that he loved her and nothing would change that. No one believed it would work esc. Prue, but when she died Paige felt the same way about Cole, she knew something was up, and he wasn't good but still evil. Cole did have a good side to him, it's just his demonic side was more powerful and over powering. Of course Phoebe and Cole married. Phoebe became pregnant, although it was a potion that Cole and the Seer made to get her pregnant. They were trying to turn Phoebe evil, and soon she had to choose between her husband and her family. Of course she chose her family, and vanquished Cole who was now the Source. The seer tried to go against the Charmed Ones and take back the baby that was inside of Phoebe, but he had way to much power over her and he killed her and all the underworld. But Cole soon came back, because he stole powers from the wastelands. When he came back he was determined to get Phoebe back at whatever costs. She still loved him, but she could never be with him it could never work, so she kept trying to get him to leave her. He was now immortal and he couldn't stand it any longer, so finally he conjured up a spell, and he was able to turn back the time, to where Paige wasn't suppose to be alive, but some how she sneezed at the exact moment that he was doing the spell, and she somehow morphed to that time with him. At this time, Piper and Phoebe didn't even know Paige. But Paige found a way to explain to them what was going on, and they were able to vanquish Cole, forever!