Thales of Miletus, the acknowledged founder of Greek mathematics and philosophy, was also an astronomer, and is the first known Greek scientist. Born about 640 B.C.E. at Miletus in Asia Minor, the primary city of the Ionian coast, it is understood that he is of Phoenician descent; his parents being Examius and Cleobuline. Early in life, Thales engaged in commerce as a merchant, and was unusually successful. Aristotle (c. 340 B.C.E.) tells of a tale how one winter, when the stars promised a plentiful crop of olives, Thales contracted out all the oil presses from Miletus and Chios. When a big olive season transpired, he thus rented the presses in the following autumn and made a rather large profit. During his middle life, he was a statesman and eventually became a mathematician, astronomer and philosopher for his later years. He is said to have traveled quite extensively to such places including Crete, Egypt and Asia. On his journey to Egypt, possibly for merchant purposes, he learned during his leisure time, the knowledge of the Egyptians on mathematics and land surveying. Plutarch remarked that he was somewhat older when he returned back to Miletus.

Thales was familiar with the astronomy of the Babylonians, possibly from the Chaldean records. It is reported that he predicted and announced beforehand, using Egyptian registers, an eclipse of the Sun. It is known that this solar eclipse took place in at least the year he predicted. On May 28th, 585 B.C., during a great battle on the Halys, between the Medes and the Lydians, the eclipse took place. Herodotus wrote, "...day was all of a sudden changed into night. This event had been foretold by Thales, the Milesian, who forewarned the Ionians of it, fixing for it the very year in which it took place. The Medes and Lydians, when they observed the change, ceased fighting, and were alike anxious to have terms of peace agreed upon." Thales seemed to have indulged his taste to learn, thus founding the Ionian School. As his reputation grew, he was enrolled as the first of the Seven Wise Men. Plutarch said "Thales apparently, was the only one of these whose wisdom stepped, in speculation, beyond the limits of practical utility: the rest acquired the name of wisdom in politics." Thales believed water was the origin of all things and that the earth was a flat disc, simply floating on water. Thales had a more universal and philosophical wisdom; he asked for the origin of things. Plato told of Thales falling into a well while gazing at the stars, and that a Thracian slave-girl laughed at him, saying "he wanted to know what happens in the heavens but he did not want to see what was in front of his own feet". At his death, the leadership of the Ionian school passed on to Anaximander, probably a pupil of his, responsible for bringing to use in Greek, the gnomon, an instrument used for determining noon, the solstices and the equinoxes. Thales died about 542 B.C.E. in his home town of Miletus.