Ibn Khaldun is one of the rare Muslim intellectuals who is famous in the West, cited by everyone from Arnold Toynbee to Ronald Reagan.  He has been called the father of the modern discipline of History, as well as the Social Sciences in general.  All these claims have been disputed.  Nonetheless, Ibn Khaldun gave the world a theory about the rise and fall of empires that did not depend on mystical or religious explanations, and has become a part of our understanding of History today.