Aleister Crowley was an English occultist, ceremonial magician, poet, painter, novelist, and mountaineer. He founded the religion of Thelema, identifying himself as the prophet entrusted with guiding humanity into the Æon of Horus in the early 20th century.
In 1898, he joined the esoteric Hermetic Order of the Golden Dawn, where he was trained in ceremonial magic by Samuel Liddell MacGregor Mathers and Allan Bennett. He married Rose Edith Kelly and in 1904 they honeymooned in Cairo, Egypt, where Crowley claimed to have been contacted by a supernatural entity named Aiwass, who provided him with The Book of the Law, a sacred text that served as the basis for Thelema.
Announcing the start of the Æon of Horus, The Book declared that its followers should "Do what thou wilt" and seek to align themselves with their True Will through the practice of magic.
Thelemite groups were established in Britain, Australia, and North America. Crowley spent the First World War in the United States, where he took up painting and campaigned for the German war effort against Britain, later revealing that he had infiltrated the pro-German movement to assist the British intelligence services. Some biographers allege that he remained a spy throughout his life.
In 1920, he established the Abbey of Thelema, a religious commune in Cefalù, Sicily where he lived with various followers. His libertine lifestyle led to denunciations in the British press, and the Italian government evicted him in 1923. He divided the following two decades between France, Germany, and England, and continued to promote Thelema until his death.
Crowley believed in the objective existence of magic, which he chose to spell "Magick", an older archaic spelling of the word. In his book Magick in Theory and Practice, Crowley defined Magick as "the Science and Art of causing change to occur in conformity with Will".
One of his better-known converts was Jack Parsons, the American chemist, rocket-engineer, and occultist. L. Ron Hubbard, sci-fi writer and founder of Scientology, was also involved in Thelema in the 1940s. Crowley was also featured as one of the faces on The Beatles' Sgt. Pepper's Lonely Hearts Club Band album cover in the upper lefthand corner.
Crowley gained widespread notoriety during his lifetime, being a recreational drug experimenter and being openly bisexual. He has been called "the wickedest man in the world" and labeled as a Satanist by the popular press. Crowley has remained a highly influential figure over Western esotericism and the counterculture, and continues to be considered a prophet in Thelema.