Epicurus (341–270 BC)
Epicurus was a Greek philosopher who was born on the Ionian island of Samos. Eventually, he moved to Athens where he opened a school of philosophy in a garden that he had bought and laid out for the purpose. He developed further the doctrine of atomism, as expounded by Leucippus and Democritus, including the idea that life exists elsewhere in the universe. In his Letter to Herodotus, he writes:
[T]here are infinite worlds both like and unlike this world of ours ... we must believe that in all worlds there are living creatures and plants and other things we see in this world...
Everything, he believed, could be explained in terms of natural causes. As for the gods, he taught that they existed only in the spaces between worlds, having no interest at all in human affairs.
Epicurus preached a materialist, sensationalistic philosophy which emphasized the positive things in life and remained popular for more than 600 years.