Serial killer Henry Lee Lucas in prison in Huntsville, Texas, in 1998.

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When it comes to naming the world's most prolific serial killer, some boundaries must be established. As Soviet dictator from 1924 to 1953, Josef Stalin was responsible for the deaths of millions of citizens who died from starvation and internment in gulags (forced labor camps) [source: BBC]. Adolph Hitler's genocidal bent led to the murders of nearly 21 million people (not including those combatants who died fighting the German army) [source: University of Hawaii].

But these men, and others like them who've issued wholesale execution orders, did not directly murder the people who died under their authority. And to be considered a serial killer, one must have personally murdered three or more people [source: Princeton]. Even under the parameters of this definition, there have been some pretty prolific serial killers.

Henry Lee Lucas confessed to killing hundreds of people, but he was linked only to three to 12 victims (in addition to his mother, whom he beat to death). Lucas said he falsely confessed to other murders because he enjoyed toying with law enforcement [source: New York Times]. Canadian pig farmer Robert Pickton was accused of murdering 26 women. When he was caught, Pickton said that his goal was to kill 50 [source: BBC]. The most prolific serial killer in recent history, Colombian Pedro Lopez, murdered 300 people, mainly young girls. He was freed from prison in Ecuador in 1998 [source: The Telegraph].

Serial killers tend to be men by an overwhelming margin. In fact, there's no definitive profile for female serial killers [source: LSU]. But if history and evidential testimony are correct, a woman is the most prolific serial killer of all time. Erzsébet (Elizabeth) Bathory, a Hungarian countess, is believed to have killed as many as 650 people during the 54 years she lived. And exactly how the world's most prolific serial killer took the lives of her victims has proven grisly fodder for storytellers. Bram Stoker is believed to have been inspired by the countess: His Count Dracula is supposedly a hybrid of Wallachian prince Vlad Tepes and Bathory [source: NNDB].

Find out about some of the legends and facts surrounding Bathory, perhaps the most prolific serial killer, on the next page.