Aleister Crowley (12 October 1875 – 1 December 1947) was a British mystic, occultist, writer, poet, mountain climber and nicknamed "The Wickedest Man In the World.".

He was an influential member in some occult organisations, such as the Golden Dawn, the A∴A∴, and Ordo Templi Orientis (O.T.O.), and is better known today for his occult books and papers. He was bisexual.

Crowley also started a mystical philosophy known as Thelema, the Abbey of Thelema, and revived the term magick.