Henri Désiré Landru was a French serial killer, nicknamed the Bluebeard of Gambais. He murdered at least seven women in the village of Gambais between December 1915 and January 1919. Landru also killed at least three other women and a young man in the house he rented from December 1914 to August 1915 in the town of Vernouillet, a town 35 kilometres (22 mi) northwest of Paris. The true number of Landru's victims is suspected to be higher.

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.