Protagoras (c.480-411BC)

Philosopher from Thrace who taught in Athens and was a friend of Pericles. He was the first Sophist, and taught grammar, rhetoric as well as the interpretation of poetry.
Protagoras believed nothing was exclusively good or bad, true or false and that man is his own authority, saying that "man is the measure of all things". This has in later times sometimes been misintrepeted. What the philosopher ment was that each man's opinions differ, and what is true for one person can be false for another. Therefore, he concluded, there is no general or objective truth.
According to Plato, Protagoras stated that the punishment for a crime is executed in order to prevent the same crime from happening again, and not for revenge. Although a celebrated teacher, Protagoras was finally charged with atheism and drowned fleeing to Sicily. Fragments of his works Truth and On the Gods have survived.