Serial Killers are viewed as a threat because of how evil, disturbed, and crazy their actions are towards other individuals or animals. Although seen as wicked, we are always drawn and fascinated by how these individuals operate. We want to know their stories and how do these horrid individuals operate. What makes a serial killer slay and what motivates them to catch and kill a prey? To satisfy your interest in these villains, here are 20 of the most notorious serial killers of all time.