Aleister Crowley (1875-1947) was the most widely read author in 20th-century occultism. He single-handedly redefined magic as a field of inquiry and endeavor through his books and the order that he led--the A. A. and the O. T. O. He is the author several books including The Book of the Law, 777 & Other Qabalistic Writings, and The Book of Thoth.