He discovered gravity. Read this from Wikipedia:
Sir Isaac Newton, FRS (4 January 1643 – 31 March 1727 [OS: 25 December 1642 – 20 March 1727]) was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian and one of the most influential men in human history. His Philosophiæ Naturalis Principia Mathematica, published in 1687, is considered to be among the most influential books in the history of science, laying the groundwork for most of classical mechanics. In this work, Newton described universal gravitation and the three laws of motion which dominated the scientific view of the physical universe for the next three centuries. Newton showed that the motions of objects on Earth and of celestial bodies are governed by the same set of natural laws by demonstrating the consistency between Kepler's laws of planetary motion and his theory of gravitation, thus removing the last doubts about heliocentrism and advancing the scientific revolution.
|Includes CC-BY-SA content from Wikipedia's Isaac_Newton article (authors)|
He did a lot of research into alchemy, which came to nothing.
He also invented the ridged ('milled') edges seen on some coins, to deter clipping, and worked with the Royal Mint to send forgers to the gallows. He had viscous arguments with Hooke (another scientist), and 'took great pleasure in breaking Leibniz's heart' (Leibniz did pioneering work on calculus, including inventing the name). By all accounts, Newton was not a nice man.