Quietly brilliant, fiercely practical. Oenopides of Chios (fl. 5th century BCE) made his mark by calculating the obliquity of the ecliptic and figuring out how to align altars with the heavens — because even sacrifices need good math. He dabbled in geometry and astronomy, and may have introduced the idea of constructing figures with straightedge and compass alone. Not flashy, but foundational. Oenopides gave Greek science a bit more structure and a lot more precision.