Milton William "Bill" Cooper (May 6, 1943 – November 5, 2001) was an American conspiracy theorist, radio broadcaster, and author known for his 1991 book Behold a Pale Horse, in which he warned of multiple global conspiracies, some involving extraterrestrial life. 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". Cooper was killed in 2001 by sheriff's deputies after he shot at them during an attempted arrest.
Little is known about Cooper's background and education, beyond the information supplied in his own accounts. He claimed to have served in the United States Navy, the United States Air Force, and Naval Intelligence until his discharge in 1975; however, public records only indicate a period of service in the Navy with a ratings code of E-5/Sergeant (Petty officer second class in the Navy), including a tour of duty in Vietnam with two service medals. At the end of the war, while working in naval intelligence, Cooper served on a briefing team for Admiral Bernard A. Clarey. He then attended a junior college in California, and worked for several technical and vocational schools before making his conspiracy theories known, beginning in 1988. Cooper expanded the speculations of earlier conspiracists by incorporating government involvement with extraterrestrials as a central theme.
In the Summer of 1988, Cooper made his first public comments on the ParaNet Bulletin Board System, an early UFO message board. According to Cooper's first post, in 1966 he was serving aboard the USS Tiru when he and fellow Navy personnel witnessed a metal craft "larger than a football field" repeatedly enter and exit the water. Cooper claimed he was instructed by superiors to never speak about the incident. Biographer Mark Jacobson argues "the Tiru incident itself would not have done much to make Cooper's name in ufology. That opportunity came only a few days later" when he was contacted by fellow ParaNet poster John Lear.