&quot;The first known person to question the whole “speed of light is infinite” thing was the 5th century BC philosopher Empedocles&quot;<p>If you want your mind blown, there also was a physicist in the 20th century who questioned whether or not the speed of light was directionally invariant (isotropic).  So the speed of light going one way versus the other might be different.  This results in a different set of transformations, the Tangherlini transformations, that govern the structure of spacetime.