Serial killers are individual people who have a history of multiple slayings of individuals usually unknown to them beforehand. Their crimes are committed as a result of a compulsion that invariably has roots in the killer's (often dysfunctional) youth, as opposed to those who are motivated by financial gain (e.g., contract killers) or ideological/political motivations (e.g., terrorist).
For articles about people who have murdered two or more people in a single incident see category:mass murderers.
