Aleister Crowley, born Edward Alexander Crowley, was a British occultist, writer, mountaineer, philosopher, poet, and mystic. He was an influential member in several occult organizations, including the Golden Dawn, the A∴A∴, and Ordo Templi Orientis (O.T.O.), and is best known today for his occult writings, especially "The Book of the Law", the central sacred text of Thelema.