William of Ockham (c. 1285-1349): English medieval philosopher known as "the subtle doctor." Ockham was a Franciscan who clashed with the pope and was forced to flee to Pisa and finally Munich because of his criticisms of arbitrary papal power. He is known for his rejection of real universals and is often called the father of nominalism, although many scholars claim that he was really a conceptualist. Ockham is also famous for "Ockham's razor," or the principle of parsimony, which says that "entities should not be multiplied beyond necessity." Though that phrase is not actually from Ockham's writings, it is associated with him because of his characteristic style of philosophizing.1
1. C.Stephen Evans, Pocket Dictionary of Apologetics & Philosophy of Religion (Downers Grove, IL: InterVarsity Press, 2002), pp. 83-84.