Aleister Crowley 1899 Aleister Crowley ( 12 October 1875 – 1 December 1947), born Edward Alexander Crowley, and also known as both Frater Perdurabo and The Great Beast 666, was an English occultist, mystic, ceremonial magician, poet and mountaineer, who was responsible for founding the religious philosophy of Thelema. In his role as the founder of the Thelemite philosophy, he came to see himself as the prophet who was entrusted with informing humanity that it was entering the new Aeon of Horus in the early 20th century.