https://www.findagrave.com/memorial/32578338/_
Someone posted a shot of his grave site, and this website confirms he was QMI (Q MILITARY INTELLIGENCE) US NAVY.
His book was referenced by Q early on as a book to reference to.
From site:
Milton William Cooper was a published author, radio show host, producer, and lecturer. He was a veteran of the United States Air Force and the United States Navy, where he was a member of the Office of Naval Security and Intelligence, serving in Vietnam. During his time of service, he was awarded several medals for his leadership and heroism during combat, including two with "V" for Valor. After his military service, William attended Long Beach City College where he earned an Associate of Science Degree in Photography. He founded the Absolute Image Studio and Gallery of Fine Art Photography in Long Beach, California. He later held the position of Executive Director of Adelphi Business College, Pacific Coast Technical Institute, and National Technical College. Later in his life, he produced several documentaries covering subjects such as the Kennedy assassination and secret black projects that have built flying disk shaped craft. William was well known for his knowledge and expertise on the subject of UFO's. He was also an international radio personality broadcasting "The Hour of The Time" worldwide on short-wave radio. He is the author of "Behold a Pale Horse." The book has become the best selling underground book of all time. Cooper was a world class lecturer, one of the few other than superstars, monarchs, and Popes who have appeared at Wembley Arena in London. William Cooper, Trustee, founded for Harvest Trust, the CAJI News Service, VERITAS, a national full size newspaper, The Intelligence Service, and Harvest Publications. He also helped over 700 low power FM affiliate stations get equipped and on the air… including the station he managed as Trustee for the Independence Foundation Trust, 101.1 FM in Eagar, Arizona. Under his leadership Harvest Trust ventured into the publishing trade. The first book under the Harvest Trust imprint was Oklahoma City: Day One by Michele Marie Moore… the definitive classic on the Oklahoma City bombing of the Alfred P. Murrah Federal Building on April 19, 1995. Shortly after the bombing of the Murrah Building, Rush Limbaugh read a White House memo by Bill Clinton during his broadcast which named William Cooper, "…the most dangerous radio host in America". This comment is believed to be a direct result of Mr. Cooper's radio show, where he plainly pointed out the discrepancies and inconsistencies in the government's account of the Murrah Building attack. Mr. Cooper considered President Clinton's pronouncement the greatest compliment that he ever received. In November of 2001, Milton William Cooper was killed in a controversial shootout with the Apache County, Arizona Sheriff's Department during a raid on his home. Deputies were attempting to serve a warrant for his arrest.