Ghostface aka Piper Shaw - Scream
Piper Shaw donned a Ghostface mask to seek revenge upon her father's death and upon her mother for giving her up for adoption and upon her sister, Emma, for being lucky enough to grow up with mom. Of course, she wasn't the only killer...so what's the motive for the other kills? We don't know yet, but there were a lot of kills that had nothing to do with Emma and her mom...
Henry Dunn - Harper's Island
Henry Dunn might not fit into this category as perfectly as we might wish, but dammit, he's being included. Henry went on a killing spree on an island during the weekend before his wedding killing around 20 people in cahoots with his birth father. Poor Henry was given up for adoption, couldn't handle that news, and unknowingly fell in love with his half sister. Terribly disturbed, he just wanted what he wanted and would do what he needed to get her, and she was't his bride to be. The mystery of it all and the pain of watching characters we grew to love die helped propel Harper's Island to one of the best summer series in a very long time.
The Reaper aka George Foyet - Criminal Minds
George Foyet was a cunning sociopath who could compel the authorities into surrendering. He loved power and control and didn't have a specific type of victim, making it diffiult to track him. He put not only Morgan in danger, stealing his credentials, but Foyet was ultimately beat to death by Hotch for killing his ex wife Haley when he planned an attack on the entire family. Rot in hell!
Gormogon and His Apprentice Zack Addy - Bones
This was a case of the serial killer being nowhere near as frightening as what the mystique of his capabilites could do turned out to be. He lured beloved Jeffersonian intern Zack Addy into helping him as his apprentice. While the real Gormogon, who was discovered by way of a tapestry inspired by secret societies and made of teeth scarred bones, was seen only briefly, it was the destruction of Zach that changed things on Bones forever.
The Salem Strangler aka Jake Kositchek - Days of Our Lives
The Salem Strangler stalked and killed many in the early 80s, including Marlena's twin sister, Samantha Evans. He was caught and killed by Roman Brady. Ironically, the actor who played his brother, Chris Kositchek returned to Salem later as Roman Brady. The Salem Strangler was the first serial killer in tiny Salem, leading to the Salem Slasher, The Riverfront Knifer, Salem Stalker, and others, including the current Red Tie Killer, who is now terrifying residents of Salem just as the Salem Strangler did decades ago.
Norman Bates - Bates Motel
Norman Bates has only just begun killing in the Bates Motel world, but he'll continue on, thanks to an abnormally close relationship with his mother. She's his best friend. He'll certainly grow to be more prolific as time goes on, but for now, he'll take people out when he's overly stressed and "mother" takes over his more timid nature.