Democritus did not believe in gods nor an afterlife. He is sometimes called the laughing philosopher, because he found life much more cheerful without what he considered to be these depressing superstitions. It would be many centuries before these ideas would again become well-known. He is the most famous of the group of philosophers known as the sophists. Because some of these professors taught little more than how to win arguments in court, and did so for exorbitant fees, the name has become somewhat derogatory.
Sophistry now means argument for argument s sake, or for the sake of personal gain.
Protagorus, although his teaching fees were in fact high, was a serious philosopher. He can be credited with founding the science of grammar, being the first to distinguish the various conjugations of verbs and declensions of nouns. He was a skeptic, and believed that there were no ultimate truths, that truth is a relative, subjective thing. Man is the measure of all things, is his most famous quote, meaning that things are what we say they are. Apparently, he drowned on his way to Sicily.