Protagoras was born around 490-486 BCE in Abdera, and he probably died around 422-417 BCE. He traveled around Greece as the first Sophist (one who lectured and gave private courses on rhetoric for a fee), and became very wealthy by it, at some point charging a fee of 100 minae. During the 450's or early 440's BCE he visited Athens and met Pericles. Eventually Pericles invited Protagoras back to Athens in 444 BCE to draft a law code for the city-state of Thurii. Protagoras would have visited Athens a number of times throughout his life. Callias was an extremely wealthy Athenian who apparently gave Protagoras hospitality and protection when he was in Athens. In the Meno, Plato has Socrates mention Protagoras, "I believe he was nearly seventy when he died and had practiced his craft for forty years. During all that time to this very day his reputation has stood high." He was the first to put forth the theory of relativism.
Some of his extant quotes are:
“Man is the measure of all things, of things that are that they are, and of things that are not that they are not.”
"A thing is to me such as it appears to me, and is to you such as it appears to you."
"About the gods, I have no means of knowing either that they exist or that they do not exist."
"Even though his sons were fine young men and died within seven days of each other, he endured it free from grief; for he maintained his calm, and this brought him great benefits every day, in terms of happiness, freedom from pain and good reputation amongst the multitude. For every man who saw Pericles bearing his sorrows in so steadfast a way thought that he was both high-minded and brave, and even more powerful than themselves, knowing very well that they themselves would be helpless in such circumstances."
Meno 91d, 91e
Theatetus pg. 866, 870-876, 151e-152e, 166d-167b
Cratylus 385e, 386c