Born in 500 BC, the son of Hegesiboulis and native of Klazomenae in Thrace (near modern Izmir, Turkey), Anaxagoras was the first philosopher to make his home in Athens. There, as a friend of Pericles, Anaxagoras attracted the attention of men of scientific interests.

His most important contribution to philosophy was his doctrine of the origin of all things. He held that all matter had existed originally as atoms, or molecules; that these atoms, infinitely numerous and infinitesimally small, had existed from all eternity and that order was first produced out of this infinite chaos of minute atoms through the influence and operation of an eternal intelligence (nous). He also believed that all bodies are simply aggregations of atoms, for example, that a bar of gold, iron, or copper is composed of inconceivably minute particles of the same materials.

Anaxagoras marks a great turning point in the history of Greek philosophy. His doctrine of the nous was adopted by the Greek philosopher Aristotle; his doctrine of atoms prepared the way for the atomic theory of the Greek philosopher Democritus. Only fragments of Anaxagoras' most important work, On Nature, have survived.

In 434 BC the philosopher was tried for impiety, the charge being that he taught that the sun was a hot stone and the moon was earth. It is probable that the suit had political implications and that it was brought to embarrass Anaxagoras' patron, Pericles.

Forced to leave Athens, Anaxagoras lived in Lampsakos, where he established a school and where an altar was erected in his memory.

He is described by Aristotle as 'older in years, younger in works than Empedocles".