Whose idea first explained why planets move in ellipses around the Sun under gravity?

Newton showed that the same gravity that makes objects fall also governs planetary motion. In his Principia of 1687, he demonstrated that an inverse-square force leads to elliptical orbits, matching Kepler’s laws. This was a major unification in science, linking terrestrial and celestial mechanics. Newton’s work made it possible to calculate orbits with precision and changed astronomy permanently.