Let's start with a quiz:
Undeservedly the first man made it onto the top ten BBC Millennium list (10th) while arguably James Clerk Maxwell, the gentleman to the right, considerably improved the lot of humanity.
He changed physics forever, single-handedly undermining the very foundation of the science when developing his theory of electromagnetism in the early 1860s.
At first, nobody noticed.
Maxwell predicted the existence of electromagnetic waves (but didn’t live to see this prediction experimentally verified) and correctly identified light with electromagnetic waves. This seemingly settled an old score once and for all in favor of Christian Huygens theory of light and relegated Newton’s corpuscular theory (proposed in his famous work, Opticks) to the dustbin of history.
There was just one little problem, and over time it grew so big it could no longer be ignored.
Until then all natural laws were well behaved. They didn’t discriminate against you if you happened to live on another star that zips through the cosmos at a different rate of speed than our solar system.
Physics laws are usually written down with respect to inertial frames of references (i.e. usually represented by a simple cartesian grid). Inertial means that these systems can have relative motion but don't accelerate. Natural laws could always be transformed between such reference systems so that by just representing the coordinates of system 1 in those of system 2 you again retain the exact same form of your equations (this is referred to as being invariant under Galilean transformations).
Maxwell’s equations did not conform and steadfastly refused to follow these iron-clad transformation laws. And this wasn't the only problem; in combination with statistical thermodynamics, electrodynamics also predicted that a hot object should radiate an infinite amount of energy, a peculiarity know as the ultraviolet catastrophe.
These two issues were the seeds for the main physics revolutions of the last century. The first one directly lead to Special Relativity (one could even argue that this theory was already hidden within the Maxwell equations). While the second one required field quantitization in order to be fixed and spawned modern Quantum Mechanics.
It all started with this unlikely revolutionary whose life was cut short at age 48 (succumbing to the same kind of cancer that killed his mother).
Maxwell, like no other, demonstrated the predictive power of mathematical physics. One wishes he could have lived to see Heinrich Hertz confirm the existence of electromagtnetic waves - he would have been 55 at that time. But no human life span would have sufficed to see his first major insight verified:
A calculation early in his career conclusively demonstrated that the rings of Saturn had to be made up of small "brick-bat" rocks. It wasn't until the Voyager probes encountered the planet in 1980/81 that he was proven right. Really, they should be called Maxwell's rings.