Aristotle

Aristotle (384-322 BC) is the most comprehensive thinker in Western intellectual history — student of Plato, tutor of Alexander the Great, and founder of the Lyceum in Athens. His Organon invented formal logic; his Nicomachean Ethics remains the foundation of every university ethics course; his biological treatises described over 500 species through direct observation and made him the father of zoology. Dante simply called him "the master of those who know." His ideas so completely dominated medieval European and Islamic thought that scholars called him simply "The Philosopher" — no name required. Aquinas built his theology on Aristotelian foundations, and Newton spent years arguing with conclusions Aristotle had reached 2,000 years earlier.