Aleister Crowley (10/12/1875 – 12/1/1947) was an English born oculist and writer. Though it's been almost 70 years since his death his influence is present in much of modern culture. An author of many books his most revered is the Book Of The Law also known as Liber AL vel Legis. By Crowley's own testimony the book was transcribed to him while in Egypt in 1904 by an entity named Awaiss who was a messenger for the god Horus. You most likely have heard or seen the phrase "Do What Thou Wilt Shall Be The Whole Of The Law" the famous mantra from the book.
Crowley's influence is widespread, he formed his own religion Thelema or O.T.O. (Ordo Templi Orientis), which is still ongoing today. There are multiple chapters in every state in the USA as well as worldwide yet the official membership is undisclosed and no one admits to membership. Thelema is an occult religion the lives by the mantra "Do What Thou Wilt". It is a mixture of occultism, Yoga, Eastern and Western Mysticism, Qabalah, ceremonial sex magic and ritual sacrifice. Yes ritual HUMAN sacrifice.
"For the highest spiritual working one must accordingly choose that victim which contains the greatest and purest force. A male child of perfect innocence and high intelligence is the most satisfactory and suitable victim."
- Magick In Theory And Practice, by Aleister Crowley
Crowley referred to him self as both the "Wickedest Man in the World" and "The Beast 666". He was extremely antagonistic to religion and Christianity as are his followers.
Still he was revered by the likes of The Beatles, The Doors, Led Zeppelin and today artist such as Jay Z, Kanye West and Marilyn Manson among others. Once introduced to black magic and the powers and pleasures that come, people are attracted, this is the appeal of Crowley and the occult in general.
This is just a brief overview of a very complex and evil individual. We implore you to research the subject further, you no doubt will be amazed and appalled at the wickedness we left out.