Milton William "Bill" Cooper (May 6, 1943 - November 6, 2001) was an American conspiracy theorist, radio broadcaster, and author best known for his 1991 book Behold a Pale Horse, in which he warned of multiple global conspiracies, some involving extraterrestrial aliens. Cooper also described HIV/AIDS as a man-made disease used to target blacks, Hispanics, and homosexuals, and that a cure was made before it was implemented. He has been described as a "militia theoretician".
As Cooper moved away from the UFOlogy community and toward the militia and anti-government subculture in the late 1990s, he became convinced that he was being personally targeted by President Bill Clinton and the Internal Revenue Service. In July 1998 he was charged with tax evasion; an arrest warrant was issued, but Cooper eluded repeated attempts to serve it. In 2000, he was named a "major fugitive" by the United States Marshals Service.
On November 5, 2001, Apache County sheriff's deputies attempted to arrest Cooper at his Eagar, Arizona home on charges of aggravated assault with a deadly weapon and endangerment stemming from disputes with local residents. After an exchange of gunfire during which Cooper shot one of the deputies in the head, Cooper was fatally shot. Federal authorities reported that Cooper had spent years evading execution of the 1998 arrest warrant, and according to a spokesman for the Marshals Service, he vowed that "he would not be taken alive".