Protagoras (c. 480-c. 411 bc), Greek philosopher, born in Abdera, Thrace. About 445 bc he moved to Athens, where he became a friend of the statesman Pericles and won great fame as a teacher and philosopher. Protagoras was the first thinker to call himself a sophist and to teach for money, receiving large sums from his pupils. He gave instruction in grammar, rhetoric, and the interpretation of poetry. His chief works, of which only a few fragments have survived, were entitled Truth and On the Gods. The basis of his speculation was the doctrine that nothing is absolutely good or bad, true or false, and that each individual is therefore his or her own final authority; this belief is summed up in his saying: “Man is the measure of all things.” Charged with impiety, Protagoras fled into exile; he drowned on his way to Sicily. Two celebrated dialogues, Theaetetus and Protagoras by Plato, refuted the doctrines of Protagoras.