Penn

"You made me! You taught me! You approved of me in ways my mortal father never did! You're my real father, Angelus." ~ Penn

Penn was the chief antagonist of the Angel episode "Somnambulist" and was a vampire who had been sired by Angelus himself - giving him a unique psychic link with Angel that allowed him to see Penn's murders and track the insane vampire down to end his reign of terror once and for all.

History
Penn lived around the late 1700s and had been a young Puritan up until Angelus made him a vampire. 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 cheeks after 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 while striking Penn in the heart. When Angel pointed out Kate missed his heart while killing Penn, she replied that she did so on purpose.