In addition to his literary pursuits, Cooper was also the host of his own worldwide shortwave radio show,
Hour of the Time, as well as a political activist known for his court battles with the Internal Revenue Service (IRS) despite strong efforts to dissuade him from pursuing his case. He also operated a dial-up bulletin board system (BBS) known as
The Citizens Agency for Joint Intelligence (CAJI).
He and Wayne Bentson co-researched the related CAJI News Service brief titled
BATF/IRS...Criminal Fraud, a history of alleged crimes committed by the Internal Revenue Service, Bureau of Alcohol, Tobacco and Firearms and the Department of the Treasury. In an article published in Veritas magazine (issue #6, September 1995), Cooper asserted that the IRS is actually the same organization as the Bureau of Alcohol, Tobacco and Firearms.
He had also produced several documentaries covering subjects such as the John F. Kennedy assassination and government 'black projects'.
Cooper's detractors labeled him a conspiracy theorist because of his publications, a charge Cooper did not deny, arguing this:
Investigation of the alleged Internal Revenue Service and the Bureau of Alcohol, Tobacco and Firearms has disclosed a broad, premeditated conspiracy to defraud the Citizens of the United States of America. Examination of the United States Code, the Code of Federal Regulations, the Statutes at Large, Congressional Record, the Federal Register, and Internal Revenue manuals too numerous to list, reveals a crime of such magnitude that words cannot adequately describe the betrayal of the American people. What we uncovered has clearly been designed to circumvent the limitations of the Constitution for the United States of America and to implement the Communist Manifesto within the 50 States. Marx and Engels claimed that, in the effort to create a classless society, a "graduated income tax" could be used as a weapon to destroy the middle class. [ . . . ] Through the clever use of language, the government promotes the fraud.
William Cooper founded Harvest Trust, the CAJI News Service, Veritas newspaper, The Intelligence Service, and Harvest Publications. Under his leadership Harvest Trust ventured into publishing. The first book under the Harvest Trust imprint was
Oklahoma City: Day One (ISBN 0-9653307-1-0), by Michele Marie Moore about the Oklahoma City bombing. In 1998 Veritas and Harvest Publications was sold to Hallmark Creative Corporation along with the copyright and all rights to all written material produced or ever to be produced by William Cooper including
Behold A Pale Horse and
Oklahoma City: Day One. Hallmark Creative Corporation has contracted to ensure this material is always available to the public.
An advocate of free radio, Cooper operated the unlicensed Independence Foundation Trust at 101.1 FM in Eagar, Arizona. He boasted of having helped more than 700 low-power FM affiliate stations get equipped and on the air.