Thales of Miletus (; , Thales; 624 – c. 546 BC) was a pre-Socratic Greek philosopher, mathematician and astronomer from Miletus in Asia Minor, current day Milet in Turkey and one of the Seven Sages of Greece. Many, most notably Aristotle, regard him as the first philosopher in the Greek tradition. Aristotle reported Thales' hypothesis that the originating principle of nature and the nature of matter was a single material substance: water.

Thales was a Greek philosopher from Miletus.