Electromagnetic wave theory was mathematically formulated by James Clerk Maxwell in the 1860s. His famous set of equations, Maxwell's Equations, unified electricity, magnetism, and light, predicting that oscillating electric and magnetic fields propagate as waves through space at the speed of light, c.

While Huygens contributed to wave optics and Hertz later experimentally confirmed the existence of these waves, Maxwell is credited with the foundational theory.

Final Answer: Maxwell