Epicurus, 341-270 BCE.
Most of us hear the name Epicurus and think of hedonism, but that's because we're suffering from millennia of bad PR. In his time and for some centuries after, Epicurus was often mentioned in comparison with the Stoics (were they hedonists?), whose conclusions he mirrored, but for different reasons - Epicurus was a staunch atheist, rationalist and materialist in the third century B.C., and like modern atheists, concluded that this world was the important one, so live a good life (which included, among other things, physical happiness.) Of course, in the ancient Near East, such a voice was a threat to Judaism and the early Christian church, so a successful smear campaign painted him and his followers as the nihilistic thrill-seekers that so many Christians today seem to desperately want us atheists to be. The same happened to Roman materialist poet Lucretius.
Fortunately, Epicurus is getting a re-evaluation by philosophers and classicists, which is slowly but surely sweeping away the obscurantism of early Christianity's own Ministry of Truth. It's unfortunate that the philosophical schools of the ancient world come down to the present by virtue of the zeal of their followers and the containment of their teachings in a single well-branded book, rather than their direct usefulness. This article summarizes Epicurus's place in both philosophy and the theological counter-reaction he inspired.