He was born in 624 BC: just after Homer wrote the Iliad and the Odyssey and right before Judah would fall to the Babylonia in 589 BC to start the Babylonian Exile. It was the time of the great Athenian lawgiver, Solon, who, with Thales, is one of the Seven Ancient Sages, or Gnomics, of Greece. (The others: Pittacus of Mytilene, Bias of Priene, Chilon of Sparta, Cleobulus, Periander of Corinth.)
Aristotle established that Thales was the first real philosopher. He looked at the world, saw that all things change and that one body becomes another, and concluded there must be one single substance that underlies all things. This thing was water. All things, to Thales, were water. It's materialistic monism. All things consist of one (the monism part) material substance (the materialistic part).