William of Ockham was a prominent English philosopher and theologian who lived in the 14th century. He is best known for his principle of parsimony, known as Occam's Razor, which states that among competing hypotheses, the one with the fewest assumptions should be selected. Ockham was a key figure in the development of nominalism, a philosophical position that denies the existence of universals and emphasizes the individual as the primary unit of reality. His ideas had a significant impact on the fields of philosophy, theology, and science, and he is considered one of the most important medieval philosophers.