Earlier in his life, Newton demonstrated that white light is the combination of colors of light, and hypothesized that light was made up of many very small particles he dubbed "corpuscles". This notion would be resurrected by none other that Albert Einstein, with Einstein calling light particles "photons".
Newton's Laws of Motion, together with his Law of Gravity, provide the theoretical underpinnings for explaining how the Solar System is held together, and why Kepler's Laws of Planetary Motion are true. In his study of the motions of celestial bodies, he discovered important concepts like conservation of energy, and conservation of momentum.
With the possible exception of Albert Einstein, Newton is considered to be the greatest physicist of all time, singlehandedly discovering the Three Laws of Motion, and the Universal Law of Gravity. He is also credited with developing the mathematical subject of the Calculus, and making important discoveries in the field of Optics.
Sir Isaac Newton, an English physicist, mathematician and astronomer, lived from 1643 AD to 1727 AD.