Joseph Gleydson Vacher was a French serial killer and necrophile, sometimes known as "The French Ripper" or "L'éventreur du Sud-Est" owing to comparisons to the more famous Jack the Ripper murderer of London, England, in 1888. His scarred face and plain, white, handmade rabbit-fur hat composed his trademark appearance. He killed 11 to 27 people, many of whom were adolescent farm workers, between 1894 and 1897.

A serial killer is a person who murders three or more people, with the killings taking place over a significant period of time between them. The serial killers' psychological gratification is the motivation for the killings, and many serial murders involve sexual contact with the victims at different points during the murder process. The Federal Bureau of Investigation (FBI) states that the motives of serial killers can include anger, thrill-seeking, financial gain, and attention seeking, and killings may be executed as such. The victims tend to have things in common such as, demographic profile, appearance, gender or race. The FBI will focus on particular patterns that the serial killers follow throughout their murders. They will then use on the patterns they find for key clues into finding the killer along with their motives. Although a serial killer is a distinct classification that differs from that of a mass murderer, spree killer, or contract killer, there are overlaps between them.