Belgian astrophysicist Georges Henri Joseph Édouard Lemaître (1894 – 1966) was the professor of the theory of relativity at the Catholic University of Louvain. He suggested that that the recession of nearby galaxies could be explained by an expanding, rather than a static, universe. His "hypothesis of the primaeval atom", subsequently developed into the 'Big Bang' theory of the origin of the Universe. See here for a more detailed biographical sketch.