Protagoras (490-420 BC), a sophist was an atheist, a rarity those days in Greece. One of the false charges against Socrates in the Athenian judicial assembly consisting of 1000 judges was corrupting the youth by spreading atheism. Plao’s last work, LAWS, restrains the state from capital punishents except for the serious crimes, like atheism. Sophists were alien residents, considered to be robing universities. They will teach for a fee but in the fashion of Guru-dakshina that was decided by the pupil. There were no public institutions; Plato’s Academy was the first public education institution in Athens. The difference between Gurukul system and Athenian system was that in the former the student goes to the teacher and in the later the teacher goes to the student.
Plato’s one of the dialogues, is titled on his name, in which Plato credits him with having invented the role of the professional sophist or teacher of virtue. He is also believed to have created a major controversy during ancient times through his statement that man is the measure of all things. This idea was very revolutionary for the time and contrasting to other philosophical doctrines that claimed the universe was based on something objective, outside the human influence.
An alien in Athens from Thrace, originally, it is said that he originally made his living as a porter but one day he was seen by the philosopher Democritus, another radical philosopher of his time along with Heractlitus, carrying a load of small pieces of wood tied with a short cord. Democritus discovered that Protagoras had tied the load himself with such perfect geometric accuracy that it revealed him to be a mathematic prodigy. He immediately took him into his own household and taught him philosophy.
As to gods, I have no way of knowing either that they exist or do not exist, or what they are like.
Let us hold our discussion together in our own persons, making trial of the truth and of ourselves.
Man is the measure of all things.
No intelligent man believes that anybody ever willingly errs or willingly does base and evil deeds; they are well aware that all who do base and evil things do them unwillingly.
The Athenians are right to accept advice from anyone, since it is incumbent on everyone to share in that sort of excellence, or else there can be no city at all.