Sir Isaac Newton was an English mathematician, physicist, astronomer, theologian, and author who is widely recognised as one of the greatest mathematicians and most influential scientists of all time and as a key figure in the scientific revolution. His book PhilosophiƦ Naturalis Principia Mathematica, first published in 1687, established classical mechanics. Newton also made seminal contributions to optics, and shares credit with Gottfried Wilhelm Leibniz for developing the infinitesimal calculus.