A serial killer is defined as a person who murders three or more people over the course of a month or more with a “cooling-down” period between each murder. These murders are distinguished events, typically compelled by a need for psychological gratification.
Serial killers are often interpreted in four categories, distinguished by the motives that trigger the murders. The four types of serial killers are hedonistic (compelled by thrill, sexual gratification, or financial gain), power/control (the need to have complete control or gaining power over victims), mission (motivated by revenge, hatred for a specific group, or the need to cleanse the world), and visionary (psychosis, “possession”, mandated by demons or God).
This infographic by SmartAdvocate.com ranks the 50 most prolific serial killers around the world based on their number of victims.