The four fundamental forces of nature are the frictional, gravitational, electromagnetic and nuclear forces. The gravitational force happens to be the weakest among them. But at the astronomical level, where masses are enormous, this force plays an important role from initiating the birth of a star, controlling the orbits of planets to determining the structure and evolution of the entire universe.
Scientists before Newton (i.e. before the seventeenth century) believed that things fell on the earth because it was the inherent property of matter, and needed no further explanation. But Newton was not satisfied with this explanation.
Galileo made the first systematic study of falling bodies. Newton was born in the same year as Galileo died. Galileo did not know of the basic law governing gravitation. Newton was the first to realize that the weight of a body on the surface of the earth is due to the force of attraction between the body and the earth.
It required his supreme genius to realize that this attraction is only a particular case of a universal attraction between any two bodies situated anywhere in the universe. At this age of twenty-three he discovered a law now known as Newton's law of Universal Gravitation Which has had far-reaching consequences in unfolding the mysteries of nature.