Isaac Newton, the renowned English physicist, developed the theory of gravity in the late 17th century. His work, particularly in his book "Philosophiæ Naturalis Principia Mathematica," published in 1687, laid the foundation for classical mechanics. Newton proposed that every mass attracts every other mass through a force called gravity, which explains the motion of celestial bodies and objects on Earth. His laws of motion and universal gravitation transformed our understanding of the physical world and have influenced various scientific disciplines. Newton's contributions remain integral to physics and continue to be taught today.