James Clerk Maxwell, pictured left, is generally regarded as one of the greatest physicist this world has ever seen. Probably the most famous physicist of our time, Albert Einstein, was a great fan of Maxwell's work and put on record that Maxwell's work had resulted in the most profound change in the conception of reality in physics since the time of Issac Newton. So what exactly did he do that earned him such high praise?
Well, his research united electricity and magnetism into the concept of the electro-magnetic field. He proposed many other theories that weren't proved until long after his death. For instance he proposed that when a charged particle was accelerated, the radiation produced has the same velocity as that of light. This is one of the defining landmark discoveries in not just physics, but science as a whole. It helped pave the way for Einstein's theory of relativity. Maxwell's ideas also led to the other major innovation of twentieth century physics, the Quantum theory.