The man who measured the Earth with shadows and brains. Eratosthenes (c. 276–194 BCE) ran the Library of Alexandria, invented a way to find prime numbers, and figured out the Earth’s circumference using sticks, sun angles, and geometry. (He was off by just a few hundred kilometers — no GPS needed.) He called himself a philologist, but we’d call him a data nerd with style. Geography, chronology, astronomy — he basically gave science a map.