Cooper expanded the speculations of earlier conspiracists by incorporating government involvement with extraterrestrials as a central theme. 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. At the end of the war, while working in naval intelligence, Cooper served on a briefing team for Admiral Bernard A. 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.

Little is known about Cooper's background and education, beyond the information supplied in his own accounts. Cooper was killed in 2001 by sheriff's deputies after he shot at them during an attempted arrest. He has been described as a 'militia theoretician'.

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. 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. Conspiracy theorist, radio broadcaster, author

Pale Horse Rider by Mark Jacobson