The Greek-speaking mathematician of Roman Alexandria who, around 150 CE, built the most accurate model of the heavens the ancient world produced — an Earth-centered system of circles upon circles that predicted where the planets would appear and held that authority for roughly fourteen centuries until Copernicus, Kepler, and Galileo overturned it; almost nothing is known of the man, so his career is read entirely through the works that bear his name.
His picture of the cosmos was wrong, and it was one of the great scientific achievements of the ancient world. Both things are true at once. Ptolemy placed a motionless Earth at the center and set the Sun, Moon, and planets wheeling around it on a machinery of nested circles. The arrangement does not match reality. Yet it predicted where each planet would stand in the sky, months and years ahead, with an accuracy no rival could touch. For some fourteen centuries, across Greek, Arabic, and Latin learning, this was simply what the heavens were known to be. The system that Copernicus would eventually unseat was not superstition. It was rigorous, mathematical, predictive science that happened to be built on a false center.