Christian Harper is a vampire and old friend of Claire Radcliff's that she meets again in a parking lot of a grocery store. They later meet at a restaurant and catch up on old times. It is revealed that they met in 1961 or before and were both vampires at the time. Christian later invites Claire to join him in feeding on a woman outside the bar. (Breach)
With her husband at the Father/Daughter Dance, Claire sneaks off with Christian to feast on another unsuspecting blood donor, however the woman Christian has locked in his sights is Barbara Jansen, the biggest gossip girl in The Gates. Claire quickly ends the evening's meal and dissuaded Christian from taking her, likely saving her life. (The Monster Within)
After letting himself in and having a nice conversation with Claire and Dylan's daughter Emily, Claire tells him to leave. Christian invites her for dinner that very evening at his place, threatening that if she doesn't come, he will be forced to tell Dylan everything.
He offers her his family's heirloom - a ring he wants her to have as a token of his love. He confesses that not turning her all those years ago was a mistake and that he regrets it being Dylan ever since. Claire tells him with conviction that she loves Dylan and wants to continue having her life with him, but Christian doesn't take it well. Not wanting to lose Claire again, Christian captures her and bites her in the neck, breaking the bond she and Dylan had when he first sired her. That in turn, wakes Dylan up in a frenzy.
When she arrives back home early the next morning, Dylan is waiting for her. He sees the bite mark that severed the bond and asks who did it. Claire says it was Christian so Dylan demands her phone from her, which he uses to text Christian to meet up again. With a smug smirk on his face, Christian thinks he won. He is beaten unconscious by a raging Dylan.
Dylan ends up tying Christian to a tree before sunrise, proceeding to douse him water to wash off the protective ointment they use against the sun. Christian tells him they're friends, but Dylan responds that they used to be and drives off, leaving Christian to burn in the rising sun's rays.
Later it is revealed that he survived and as revenge, he kidnaps Emily. (Identity Crisis)
Dylan and Claire are desperate to find their daughter so they ask Nick Monohan to help with the search. With the help of Vanessa Buckley they find Christian's house within The Gates, trapping and interrogating him about Emily's whereabouts. He will only reveal her location if Dylan kills Nick. In a fit of rage, Dylan attacks. However, he goes straight for Christian, forcing him to tell. Emily is then discovered to be with her biological uncle.
Charismatic and charming, he is able to swoon any woman he comes in contact with. Be it his vampire nature or just his natural charm, he usually gets what he wants. He is also vindictive as seen after Dylan left him for dead and gets his way by blackmailing others as seen with Claire.