Aleister Crowley

Once the greatest magician in modern magic history, more than half of all modern magicians are affected by this man's established theories, and two-fifths of them are direct followers of his ways. Having stretched the boundaries of sorcery farther than the advances made in the last few millenia alone and written an top-class spellbooks like 'The Book of the Law', it is no surprise that many mages were outraged when this eccentric genius literally "dumped" all his magic abilities and decided to "ace it" in the field of science, thus establishing the Academy City and becoming its hidden monarch.
 * When he chose to stop using magic and was running for his life from the entire Magic Side, he met the Heaven Canceler, who eventually helped him found Academy City in a far-eastern island of Japan and also provides help in this ex-magician's new goal; to extend his lifespan for as long as possible by having all but his consciousness rely on the power of machines.