Lucretian and Epicurean Atheism From Wikipedia:
To the Greek philosopher Epicurus, the unhappiness and degradation of humans arose largely from the dread which they entertained of the power of the deities, from terror of their wrath. This wrath was supposed to be displayed by the misfortunes inflicted in this life and by the everlasting tortures that were the lot of the guilty in a future state (or, where these feelings were not strongly developed, from a vague dread of gloom and misery after death). Epicurus thus made it his mission to remove these fears, and thus to establish tranquility in the minds of his readers. To do this, Epicurus invoked the atomism of Democritus to demonstrate that the material universe was formed not by a Supreme Being, but by the mixing of elemental particles that had existed from all eternity governed by certain simple laws. He argued that the deities (whose existence he did not deny) lived forevermore in the enjoyment of absolute peace—strangers to all the passions, desires, and fears, which affect humans—and totally indifferent to the world and its inhabitants, unmoved alike by their virtues and their crimes. This meant that humans had nothing to fear from them.
So, Epicurus, while still being a philosopher without a fully-developed atheism and materialism, is a really good foundation for a philosophy that /is/.
Definitely a thinker who took an important first step, in Western philosophy, away from believing in supernatural entities and processes.