Henri Poincaré
He used his mathematical skills to look at some of the biggest problems in science in his day. He was the first person to describe in mathematical terms how three planets in orbit affect each others paths as they pass near by one another. This was called the Three Body Problem. He also tried to understand why the speed of light seems to be the fastest speed at which anything can travel in the universe. In some ways he beat the famous scientist Albert Einstein to solving this question, but Einstein gave a more complete answer. He gained fame for the discovery of the theory of relativity instead of Poincaré.