Protagoras of Abdera, fl. 5th century BC. Greek philosopher, a contemporary of Socrates, numbered with Gorgias and others among the Older Sophists. He was exiled from Athens in 415 BC for impiety. No works of his have survived; we know of him through the writings of others, and especially through Plato's dialogue Protagoras, a rather unflattering portrait of him and his disciples in conversation with Socrates.