Epicurus

Epicurus took Democritus's atomism and turned it into a way of life. If everything is atoms in the void, then there are no gods judging us, the soul is mortal, death is nothing to fear ("when death is, we are not; when we are, death is not"), and what happiness requires is simple and within reach. Once cosmic anxiety is gone, one sensible aim remains – ataraxia, tranquillity, achieved through modest pleasures and deep friendship, through the avoidance of pain and of fear.

His school, the Garden, was scandalous: it admitted women and slaves, and people lived together as equals. He is often caricatured as a hedonist, but his actual recipe for pleasure was bread, water, cheese, and good conversation. Wild pleasures, he warned, bring more pain than they prevent.

Most of his writings are lost. The richest surviving Epicurean text is the Roman poet Lucretius's De rerum natura, a six-book hexameter exposition of the whole system. Karl Marx wrote his doctoral thesis on Epicurus and Democritus.