"Anaximenes of Miletus (c. 585 – c. 528 BC) was an Ancient Greek Pre-Socratic philosopher active in the latter half of the 6th century BC. One of the three Milesian philosophers, he is identified as a younger friend or student of Anaximander. Anaximenes, like others in his school of thought, practiced material monism. This tendency to identify one specific underlying reality made up of a material thing is what Anaximenes is principally known for today."

-- Wikipedia