If we are talking about direct contribution, then the answers should be Johannes Kepler and Isaac Newton.
Isaac Newton's universal law of gravitation stemmed from Johannes Kepler's theory about the planetary orbits. Kepler figured out how planets move around the sun, but he did not explain why they do that. Isaac Newton filled in that gap in Kepler's theory.
Now I say directly because like almost all scientific theories and laws are based on works of others. Kepler's theory is based on Tycho's and Tycho's is based on Copernicus'.
