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.
S. L. MacGregor Mathers (18541918) was a prominent scholar and leader of the occult movement in Britian at the turn of the century. A lifelong fascination with mysticism and Celtic symbolism led Mathers to hold high office in the Rosicrucian Society of England, and eventually to become a founder of the Hermetic Order of the Golden Dawn. He is also well known for having been a key tutor to Aleister Crowley.