Protagoras () (ca. 490–420 BC) was a pre-Socratic Greek philosopher. He is called one of the sophists by Plato, the Greek philosopher who followed Socrates. In Plato's dialogue Protagoras, he credits Protagoras with having invented the role of the professional sophist or teacher of virtue.
Philosophy
It is thought that Protagoras used the phrase "Man is the measure of all things" (). By this, he meant that nothing is absolutely truth, but there are different truths for each person, and each person makes the truth for themselves. For example, one person might go outside on a cold day and feel some water in a bucket, and they will say that the water is warm. And another person might go outside on a hot day and feel the same water, but they will say that the water feels cold to them. Each person is right.