Protagoras was a pre-Socratic Greek philosopher. He is numbered as one of the sophists by Plato. In his dialogue Protagoras, Plato credits him with inventing the role of the professional sophist.
Protagoras also is believed to have created a major controversy during ancient times through his statement that, "Man is the measure of all things", interpreted by Plato to mean that there is no absolute truth but that which individuals deem to be the truth.
Although there is reason to question the extent of the interpretation of his arguments that has followed, that concept of individual relativity was revolutionary for the time, and contrasted with other philosophical doctrines that claimed the universe was based on something objective, outside human influence or perceptions. Wikipedia
Opening lines of Concerning the Gods (DK 80 B4).
Variant translation: "As to the Gods, I have no means of knowing either that they exist or that they do not exist, or if they do, what they are like."
As quoted in Protagoras by Plato
“There are two sides to every question.”
As quoted in Lives of Eminent Philosophers, by Diogenes Laërtius, Book IX, Sec. 51
As quoted in Theaetetus by Plato section 152a
