Actually, Einstein's reasoning wasn't to explain the Michelson-Morely results - those just supported his basic hypothesis - it was to explain what happens to the laws of physics if an observer is moving at the speed of light. His reasoning was this - if I could move at the speed of light and I looked at an electromagnetic wave moving along with me, I would see a stationary (not moving) electric field oscillating in amplitude in time, and a perpendicular stationary oscillating magnetic field. But there are no charges or currents present to cause these fields so the laws of electrodynamics, Maxwell's equations, break down. That means either the physics of electromagnetism as was understood at the time was wrong, or there was a basic problem with how we view space and time. This was the insight that led Einstein to abandon the Newtonian view of space and time - that there was an absolute measure to space and an absolute universal time. He realized space and time have to be treated equally and that if one applied the Lorentz contraction and time dilation formulas (used to rescue the aether theory and explain Michelson-Morely in that context) with the axiom that both time and space as measured by one observer is dependent on the observer's relative motion to another observer he could achieve a picture of the universe where there was no preferred spot to make observations. That means that there is no point space and time, which he renamed space-time, that is absolute rest with respect to every thing else in the universe. So now the speed of light sets a limit as to how fast any matter can travel and it preserves the laws of physic.
the answer is Maxwell.