As to the gods, I have no means of knowing either that they exist or that they do not exist. For many are the obstacles that impede knowledge, both the obscurity of the question and the shortness of human life.Ancient Greek philosophers are an interesting lot. Protagoras was among the first, pre-Socrates even, and he would have fit in well with today's skeptical crowd. He's the one who came up with "Man is the measure of all things..." We don't have the context for that quote, but it seems he wasn't impressed with the idea that there was some knowledge Out There that the gods handed down. As you can see from the above quote, he gave gods rather short shrift. He counts among the first atheists we're reliably aware of. A bold position to stake out in Athens, a city whose patron goddess was Athena, and a place where tribute meant for military endeavors had a distressing habit of ending up diverted to build bigger and better temples.
Despite his atheism, he doesn't seem to have been forced into any drinking of hemlock or other nonsense. Perhaps the authorities were afraid he'd get into a legal argument with them. A man who could spend a whole day discussing a legal technicality with Plutarch would be a formidable opponent in any court of law.