The guy who fell in a well while stargazing — and still made the history books. Thales (c. 624–546 BCE) is often called the first philosopher, not because he had all the answers, but because he thought nature had them. He said everything came from water (debatable), predicted an eclipse (impressive), and kickstarted the idea that the world runs on principles, not divine tantrums. One small step for geometry, one giant leap for critical thinking.