Ancient Greek Philosopher.
Democritus (ca. 460 – ca. 370 BC) was an Ancient Greek philosopher born in Abdera, Thrace, Greece. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated an atomic theory for the universe.
His exact contributions are difficult to disentangle from those of his mentor Leucippus, as they are often mentioned together in texts. Their speculation on atoms, taken from Leucippus, bears a passing and partial resemblance to the nineteenth-century understanding of atomic structure that has led some to regard Democritus as more of a scientist than other Greek philosophers; however their ideas rested on very different bases. Largely ignored in ancient Athens, Democritus was nevertheless well known to his fellow northern-born philosopher Aristotle. Plato is said to have disliked him so much that he wished all his books burned. Many consider Democritus to be the "father of modern science".
1.) "Most histories of atheism choose the Greek and Roman philosophers Epicurus, Democritus, and Lucretius as the first atheist writers. While these writers certainly changed the idea of God, they didn't entirely deny that gods could exist." Ancient Atheists, BBC.co.uk.