Democritus (460?–370 B.C.), a Greek philosopher. He was a Materialist, believing that the universe can be explained in terms of matter, and an Atomist, believing that all matter is composed of tiny, indestructible particles called atoms.Democritus believed that spiritual, as well as physical, things are composed of atoms. He was not the first Materialist or Atomist, but his influence was great. His writings were taken up by Epicurus, then by Lucretius, and thus are the beginning of the Materialistic theories of nature and ethics.

Democritus was born in the Thracian colony of Abdera. There is a tradition that he was blind. It is believed that he traveled and studied in Greece, Egypt, Persia, and perhaps in India before he became known as a philosopher in Abdera. Democritus believed that peace of mind is the greatest good. Only a few doubtful fragments remain of some 70 works credited to him.