Euclid of Megara

Euclid studied under Socrates in the late 5th century BC and was there when his teacher died. Afterward, he founded the Megarian school and built a philosophy around a single unshakable claim: the supreme good is one thing, eternal and unchangeable, and nothing contrary to it exists. For over a thousand years, medieval scholars mixed him up with Euclid of Alexandria, the mathematician, when copying and translating the Elements — a case of mistaken identity that outlasted the philosophy itself.