Anaxagoras was an early Greek philosopher and scientist who developed remarkable insights concerning the differentiation and structure of matter. Born around 500 B.C. in Clazomenae, now part of Turkey, Anaxagoras came from a noble and wealthy family. As legend has it, he was drawn early in life to philosophy and science and neglected his material possessions. He is noted as the person who introduced philosophy to Athens, where he moved when he was around the age of 20. According to Plato, Anaxagoras taught Pericles (c.495-429 B.C.), a Greek leader who helped develop democracy in Athens and make the city a political and cultural center of Greece. Anaxagoras may also have taught the Greek dramatist Euripides (c.484-406 B.C.) and, possibly, Socrates (c.470-399 B.C.).

Following in the footsteps of Pythagorus, Anaxagoras dealt with many questions in geometry, including the problem of squaring the circle. However, it was his theories on the creation of the solar system and matter that remain a stunning achievement in ancient Greek science and thought. Although only fragments of his only known published book still exist, these fragments and other reports reveal a keen mind that was not afraid to question widely held beliefs of the time. Anaxagoras held that an infinite number of elements made up matter, which contradicted the belief that four basic elements (earth, air, fire, and water) made up all things. His concept that "in all things there is a portion of everything..." and that the formation of different matter is caused by the union, separation, and arrangement of numerous elements anticipated the atomic theories of Democritus. Also central to his philosophy was the idea of nous (mind or reason) as the creator and driving force of the world.

Anaxagoras's insightful claim that the Sun was a hot stone instead of a god, and that the Moon reflected the Sun's light, caused him to be arrested and imprisoned. His troubles were compounded because of his friendship with Pericles, who had many political opponents. Pericles intervened and had Anaxagoras released from prison. However, Anaxagoras had to leave Athens. He returned to Asia Minor and is believed to have founded a school at Lampsacus. After his death, the citizens of Lampsacus erected an alter in his memory dedicated to mind and truth. The anniversary of his death became a holiday for school children.