Crowely founded Thelema. He was not a satanist. His religion was basically based in hermetism, western interpretations of kabala, goetia, etc. He called himself The Beast, but he did so to tweak the nose of Edwardian society and get his name in the papers. He also made it clear that "Do what thou wilt. . ." meant fullfilling one's destiny to the fullest, without interfering with the ability of others to do the same.
The late Gerald Suster and Israel Regardie both wrote fantastic bios of Crowley. I corresponded with Suster (and Michael Staley, who wrote a fab article on the Crowley-Hubbard-Parsons triangle) before his death. Both he and Staley were real gentlemen and eager to share their vast knowledge on the man and his philosophy and poetry.
Incidentally, L. Ron was kicked out of the OTO by Crowley, along with Jack Parsons. Now that's a great story.