Protagoras (Greek: Πρωταγόρας) (ca. 490– 420 BC) was a pre-Socratic Greek philosopher and's numbered as one of the sophists by Plato. In his dialogue Protagoras, Plato credits him with having invented the role of the professional sophist or teacher of virtue. He's also believed to have created a major controversy during ancient times through his statement that man's the measure of all things. This idea was very revolutionary for the time a… (More on Protagoras)