Thales of Miletus (Θαλῆς ὁ Μιλήσιος) was a pre-Socratic Hellenic philosopher and mathematician from Miletus in Asia Minor. According to Herodotus, Thales predicted the solar eclipse of May 28, 585 BC. Diogenes Laërtius quotes the chronicle of Apollodorus of Athens as saying that Thales died at the age of 78 during the 58th Olympiad (548–545 BC) and attributes his death to heat stroke while watching the games.

Thales' parents were Examyes and Cleobuline, and his family traced their line back to Kadmus, the mythological Phoenician prince of Tyre. Many, most notably Aristotle, regard him as the first philosopher in the Hellenic tradition. Thales attempted to explain natural phenomena without reference to mythology, and almost all of the other Pre-Socratic philosophers follow him in attempting to provide an explanation of ultimate substance, change, and the existence of the world without reference to mythology. He was not only a philosopher but also a businessman, and he also became involved in politics in his lifetime--like many of the Sages.

If Thales wrote down any ethical guidelines or other works of prose (a treaty entitle 'On the Solstice' and one entitled 'On the Equinox' are mentioned by other ancient writers), they have sadly been lost to us. Proclus acknowledged Thales as the discoverer of a number of specific theorems, both mathematical, geometric, and philosophical, and he is recognised as one of the--if not the--first mathematician.

Thales was esteemed in his times as an original thinker, and one who broke with tradition and not as one who conveyed existing mythologies. He never attributed organization or control of the cosmos to the Gods. Thales hypothized that water had the potentiality to change the myriad of things of which the universe is made, the botanical, physiological, meteorological and geological states--in fact, he proposed that the primary principle is water. He believed that the disk of the earth rests on water. Thales did not mention any of the Gods who were traditionally associated with the simple bodies; we do not hear of Okeanos or Gaea: we read of water and earth.

Thales has been credited with the discovery of five geometric theorems: (1) that a circle is bisected by its diameter, (2) that angles in a triangle opposite two sides of equal length are equal, (3) that opposite angles formed by intersecting straight lines are equal, (4) that the angle inscribed inside a semicircle is a right angle, and (5) that a triangle is determined if its base and the two angles at the base are given. His mathematical achievements are difficult to assess, however, because of the ancient practice of crediting particular discoveries to men with a general reputation for wisdom.