Protagoras

Protagoras was a pre-Socratic Greek philosopher and rhetorical theorist. 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 objective truth. Whatever individuals deem to be the truth, is true.
This concept of individual relativity was atypical for the time, contrasting with both popular opinion and other philosophical doctrine that reality and its truth must have an objective grounding.