Thales of Miletus was a pre-Socratic Greek philosopher, mathematician, and astronomer, often regarded as the first philosopher in Western history. He lived around 624-546 BCE and is known for his belief that water is the fundamental substance of all things. Thales is also credited with various mathematical discoveries, including theorems related to geometry. In addition to his philosophical contributions, Thales made significant advancements in astronomy. He is believed to have predicted a solar eclipse in 585 BCE and was one of the first to use geometry to solve practical problems, laying the groundwork for future mathematicians like Pythagoras and Euclid.