The reason geometry got its act together. Euclid (fl. c. 300 BCE) didn’t invent the triangle, but he made sure everyone knew exactly what it was, where it stood, and how to prove it. The Elements isn’t bedtime reading — it’s the blueprint of logical thinking, copied, studied, and feared for over two millennia. If you’ve ever said “Q.E.D.” and meant it, you’re probably standing on his shoulders. Quiet guy, loud legacy.