Wilson was interested in metaphysics and the occult. In 1971, he wrote a nonfiction book named "The Occult: A History". In it, he talked about the beliefs of Aleister Crowley, George Gurdieff, Helena Blavatsky, Kabbalah, primitive magic, Franz Mesmer, Grigori Rasputin, and Paracelsus. He also wrote a biography of Crowley, "Aleister Crowley: The Nature of the Beast". He also wrote biographies on other visionaries in spirituality and psychology. Some were about George Gurdjieff, Carl Jung, and Wilhelm Reich.