James Clerk Maxwell
James Clerk Maxwell (1831-1879) built one of the most beautiful and powerful mathematical frameworks in physics.
Maxwell unified electricity and magnetism, leading to a deeper understanding of light, by fitting all the known laws of electricity and magnetism into four equations. That provided a simple, precise description for all kinds of phenomena, from the swing of a compass needle to the spark from a brass doorknob on a cold morning. Maxwell also predicted the speed of light and explained light's nature using purely mathematical arguments - by piecing together known facts and insisting on mathematical consistency, he revealed one of the most basic properties of the universe.
Maxwell's breakthroughs opened the door to twentieth-century physics: relativity and quantum theory - our most fundamental descriptions of reality.