10. Red John (The Mentalist)
Red John is the main antagonist on The Mentalist. He lands on this list because he represents every nightmarish thing that your mind could conjure up about the most terrifying serial killers. He is an exceedingly intelligent, narcissistic, sociopath who lacks any distinguishable moral code. He will butcher men, women and children without discrimination. This complete deficit of humanity is what horrifies us most about these monsters and Red John's humanity tank is completely empty. Maintaining a flair for theater and the dramatic, this killer leaves a grisly signature at each of his crime scenes; a smiley face smeared on the wall in his victim's own blood. Every murder is well thought out and appears to be a source of euphoria for Red John. One of his various distressing qualities is his penchant for waking sleeping victims so that he can actually see their terror while he kills them. The obvious pleasure that he derives from inflicting pain on others really solidifies his place in this list. Although it can be said that Red John seemed a lot scarier when he was anonymous, Xander Berkeley did a great job in his short, unmasked stint as the serial killer. Although brief, his capture and subsequent unveiling was able to successfully convince fans of the show that they finally had their man. Berkeley was able to take one hundred plus hours of build up and bring fans a convincing psychopath.