Zachary Kralik was a serial killer/vampire and the main antagonist of the Buffy: The Vampire Slayer episode, "The Helpless".
He was portrayed by Jeff Kober.
Kralik stated that he had an abusive relationship with his mother as a child. It can be assumed she was not pleased with having a son considering that she had castrated him when he was only 10 years old.
Many years later, due to the abuse he suffered as a child, he became a serial killer who tortured and murdered more than a dozen young women. At some point, he was arrested and put in an asylum with the criminally insane, where he was sired by another vampire. As a vampire, he continued to kill and torture, though he was shunned by other vampires because of his mental state. One of his victims was his own mother. Additionally, he was dependant on anti-psychotic medication, without which he suffered extrordinary pain. He was captured by the Watchers Council and held for six years until he was chosen to be used in the Cruciamentum of Buffy Summers. They weakened Buffy and locked her in a room with him inside the "Sunnydale Arms" where she would have to defeat him using only her brains and her wits.
However, Kralik was aware of their game and decided he wouldn't "play by the rules" but that he still wanted to play regardless. So, during that night, Kralik had tricked one of the Council workers, Blair, into opening his cell by pretending to be in desperate need of his pills. While Blair was getting the pills ready, Kralik managed to release his right arm, grab Blair by the throat as he tried to give him his pills, and sire him in order to be released. He and Blair then drained and killed Blair's partner, Hobson. He then kidnapped Buffy's mother, Joyce, in order to lure Buffy, whom he wanted to sire and turn loose on Joyce. Buffy was able to trick him by taking away his pills and having him drink them with a glass of holy water, disintegrating him from the inside and killing him instantly. Rupert Giles, her watcher, killed Blair with a wooden stake.
Due to his mental state, Zachary Kralik was a sadist who enjoyed placing psychological torture. He graphically slaughtered Hobson and took dozens of photos of Joyce and placed them in a singel room at the Sunnydale Arms for Buffy to see. He also showed to be a something of a masochist, as he gained physical pleasure and even arousal from the sensation of a cross burning his torso.