Who discovered the speed of light?

The first to approximate the speed of light roughly was French physicist Armand Fizeau (1819-1896).

In 1849 Fizeau obtained a value for the speed of light that was about 5 percent too high.

Fizeau’s contemporary Jean Foucault (1819-1868) obtained the first accurate measurement (within 1 percent of the correct speed) in 1862.