Aristotle’s most famous teacher was Plato (c. 428–c. 348 BCE), who himself had been a student of Socrates (c. 470–399 BCE). Socrates, Plato, and Aristotle, whose lifetimes spanned a period of only about 150 years, remain among the most important figures in the history of Western philosophy. Aristotle’s most famous student was Philip II’s son Alexander, later to be known as Alexander the Great, a military genius who eventually conquered the entire Greek world as well as North Africa and the Middle East. Aristotle’s most important philosophical student was probably Theophrastus, who became head of the Lyceum about 323.