Isaac Newton was a scientific genius whose discoveries changed the way people thought about the world. He solved complex mathematical problems and invented the branch of mathematics called calculus. He investigated light and through experiments proved its relationship to color. And he established universal principles about how gravity, force, and motion work and are related. These principles became known as Newton's laws. Underneath Newton's public image as a genius was a man with real problems and failings—a complicated, sometimes unpleasant person whose interests and desires did not always match his legend.