George Lemaitre started thinking about the origin of the universe in the trenches during WW1. The Belgian priest went on to become an expert on Einstein's theory of relativity. applying it to the whole universe, he created a theory of the beginning of the universe that would be called The Big Bang. An insult from the atheist Fred Hoyle, it stuck. It also was proven when Hubble made his discovery of an expanding universe. The Universe was not a steady state, it had a beginning which Lemaitre could prove.
