Self-proclaimed drug and sex fiend; mostly self-published author of books on the occult; poet; founder of a cult he called Ordo Templis Orientis (OTO) based upon one of his writings, Thelema, which he claims was dictacted to him by a spirit called Aiwass.
Do what thou wilt shall be the whole of the Law is his motto for OTO. In practice, for Crowley, this meant rejecting traditional morality in favor of the life of a drug addict and brutal womanizer. ("I rave; and I rape and I rip and I rend" is a line from one of his poems. Diary of a Drug Fiend is the title of one of his books.) He claimed to identify himself with the Great Beast 666 (from the Book of Revelations) and enjoyed the appellation of "wickedest man in the world." He had two wives; both went insane. Five mistresses committed suicide. According to Martin Gardner, "scores of his concubines ended in the gutter as alcoholics, drug addicts, or in mental institutions." [Gardner, p. 198] But Crowley's allure was such that the women who were attracted to him tended already to be alcoholics, drug addicts or emotionally disturbed; so, he should not be blamed for destroying the virtue of saintly young girls. His allure seems to have consisted of two main items: he inherited a fortune and he worked hard at being strange.
Crowley's Magick in Theory and Practice is a very popular book among occultists. When Dover publishing was about to release a reprint of the book in 1990, an editor asked Martin Gardner to write a forward for the reprinting. The 1976 Dover edition had been one of their best sellers. Gardner was an unlikely choice to write the forward for Crowley's book since he had already written that Crowley was a no-good fraud in his classic Fads and Fallacies in the Name of Science. Anyway, he wrote the forward and it painted a picture of a such a cruel,despicable, egotististal mountebank that Dover decided not to reprint the book. The forward has been published in Gardner's On the Wild Side.
Crowley has had little influence on anything significant except perhaps the popularity of putting backwards messages into musical recordings. Saying things backwards derives from the notion that at the witches' Sabbath Christian prayers were said backwards in mockery. The occultist guitarist for Led Zeppelin, Jimmy Page, owns a large collection of Crowley memorabilia and bought Crowley's mansion in Boleskine, Scotland. Crowley's face is also one of many on the album cover of the Beatles' Sergeant Pepper's Lonely Hearts Club Band. While occultists such as Page are known to have put backwards "satanic" messages into recordings such as "Stairway to Heaven" ("Here's to my sweet Satan"), the Beatles used backwards musical riffs in some of their recordings, apparently more for the musical effect than as an expression of their admiration of Satan.
Says Gardner: "His reputation had been that of a man who worshipped Satan, but it was more accurately said that he worshipped no one except himself."
further reading
The Ordo Templi Orientis Phenomenon
Gardner, Martin. On the Wild Side (Amherst, N.Y.: Prometheus Books, 1992), chapter 29.