While many scientists contributed to the development of the electromagnetic theory of light, it was James Clerk Maxwell who mathematically unified electricity, magnetism, and light in a comprehensive theory.

Here's why:

* Maxwell's Equations: In the 1860s, Maxwell formulated a set of four equations that described the behavior of electric and magnetic fields. These equations predicted the existence of electromagnetic waves that travel at the speed of light.

* Speed of Light Prediction: Maxwell's equations predicted the speed of electromagnetic waves to be very close to the measured speed of light. This strong correlation suggested that light itself was an electromagnetic wave.

* Experimental Confirmation: Heinrich Hertz, in the 1880s, experimentally confirmed the existence of electromagnetic waves, thus providing strong support for Maxwell's theory.

Therefore, while others like Faraday and Ampère laid crucial groundwork, Maxwell's mathematical framework and predictions are considered the definitive confirmation of the electromagnetic theory of light.