Thales of Miletus (c. 624–546 BCE) was a pre-Socratic Greek philosopher, mathematician, and astronomer, often regarded as the first Western philosopher. He is credited with introducing a rational approach to explaining natural phenomena, departing from mythological interpretations. Thales proposed that water is the fundamental substance of all matter, emphasizing the idea of a single underlying principle (archê). He also contributed to geometry, famously predicting a solar eclipse and measuring the height of pyramids using shadows. His work laid the foundation for scientific inquiry and influenced later philosophers like Anaximander and Pythagoras.