William of Ockham was one of the most original, controversial, and provocative philosopher-theologians of the Middle Ages. His adoption of nominalism or realist conceptualism influenced many of his contemporaries, who in turn disseminated his influence to early modern authors even if they appropriated some of his ideas in ways contrary to his own intentions. He remained fundamentally an Aristotelian, but a critical one who tried to rescue what he thought was authentic Aristotelian doctrine or, alternatively, true philosophy from misinterpretations and confusions.