James Clerk Maxwell, a famous physicist of the 19th century, developed the theory of electromagnetism. His groundbreaking work unified electricity and magnetism into a single framework, introducing Maxwell's equations. These equations describe how electric and magnetic fields interact and propagate through space. Maxwell's contributions laid the foundation for many modern technologies, including radio, television, and the development of quantum mechanics. His theories also paved the way for subsequent physicists like Albert Einstein, who built on Maxwell's ideas. Maxwell is often regarded as one of the greatest physicists in history, with his work continuing to influence various scientific disciplines.