Georges Lemaître (1894-1966), the Belgian astronomer, is credited with the discovery of the Big Bang theory of the origin of the universe.
He was one of three astronomers developing non-static models of the universe. Lemaître worked out a solution to Einstein's equation but he is better known for having introduced the idea of the “primeval atom.” He stated that galaxies are fragments that have been ejected by the explosion of this atom, resulting in the expansion of the universe.