In life, Penn had been a young Puritan. According to Penn, he had issues with his father, who apparently never approved of him, even to the point of considering Angelus his real father after being sired. Similarly to his sire, Penn's first victim was his sister, subsequently going on to kill his entire family. Over the next two centuries, Penn continued his murder sprees, even adopting some of Angelus' old methods, such as carving a Christian cross on his victim's right cheek before draining them. At some point he began to deliberately seek out victims who resembled his family, killing them in order to 're-live' his past murders. He committed multiple murders in Los Angeles across various decades, leaving the city and returning to it after the hype about his last spree had faded.
When Penn last returned to the city, he was discovered by Angel, who learned about Penn's presence through an old psychic link he shared with the vampires he had created. Initially he assumed that he was committing the murders in his sleep, but after Cordelia and Wesley chained him to his bed the night before another murder, they determined that it wasn't him. Tracking Penn, Angel confronted him in front of his detective ally Kate Lockley, revealing his vampire nature to her for the first time, only for Penn to escape. Eventually discovering Penn again after Penn faked evidence suggesting he was going after a school bus, Angel and Penn fought until Kate staked Penn through Angel, impaling Angel through the stomach with a broken board while Penn was on his back. When Angel pointed out Kate missed his heart while killing Penn, she replied that she did so on purpose.
Powers and Abilities
Penn possessed the standard powers, abilities and vulnerabilities as other vampires, although due to his high age he was stronger and faster than the average vampire. His common weaknesses with other vampires included decapitation, direct sunlight or a stake through the heart. Penn, like all vampires, was unable to enter the home of a living being without to be invited.
Penn was able to move at a blurring speed in the police briefing room, which, to some, gives the question if it was unique for Penn or normal for all strong vampires. However, Angel did in fact also use rapid speed in the episode Reprise in the second season. Some fans have speculated that this scene may have simply been artistic lisence, since Penn was being observed by Kate Lockley when he moved at super-speed, and therefore Kate may have simply perceived him as moving so fast because she was unused to the supernatural and therefore had trouble processing what he was doing.