Who popularized $E=mc^2$? When asking a layman for a mathematical or physical equation you will almost certainly get the answer "$E$ equals $m$ $c$ squared". In fact, $E=mc^2$ is something like a symbol of physics in popular culture.
I'm wondering which historic events lead to the enormous popularization of this equation. There are many other important and deceptively simple equations in physics and math such as $e^{\pi i}=-1$, $E_\text{pot}=mgh$, $\nabla \cdot B=0$ and $H\psi=E\psi$, so why exactly did this one equation become so popular while the others are barely known to the public?
In particular, I would like to know when this equation became so popular. Was everybody already talking about $E=mc^2$ in the 1900s and 1910s, or did it take some time until this equation became the representative of Einstein's theories in the public?
 A: I personally think that is the answer is (at least) twofold.
Firstly, it is important to note the extraordinary amount of public attention that Einstein received after the experimental confirmation of his theory of General Relativity in 1919. Due to surprisingly extensive media coverage he became, quite literally, world famous. The reasons behind this are discussed by Abraham Pais in his biography Subtle is the Lord. Pais suggests that, Einstein, with his amazing ability to unravel the secrets of the Universe purely from reason, represented something almost divine to the general public. He stood for the incredible successes in science and theoretical physics in particular, the precision, purity and absolute truth of which carried a positive message which was warmly welcomed by the masses after the dreadful events that occurred during the First World War had caused many to despair and lose faith in humanity. Regardless of the underlying reasons, it is clear that Einstein's rise to fame was an exceedingly rare event. His fame will have contributed significantly to the interest of the general public in learning at least a little about his work, so mystifying that Eddington was famously quoted as saying only a few people in the world had attained a proper understanding of it (I cannot find the exact quote right now).
Secondly, and more speculatively, I think that this equation was 'the obvious choice' if you look at Einstein's work. Everybody is quite aware of what 'mass' is. Furthermore, if there is one concept with is both familiar to every layperson yet retains some sense of mystery it is energy. To see these universally recognized concepts related with such striking simplicity must evoke wonder in the mind of even the most scientifically ignorant mind. This gives a possible explanation why it was not the full relation $E^2=p^2c^2+m^2c^4$ that gained such fame: not everybody is familiar with momentum and what it means in an everyday situation. 
Of course, the nuclear bombs dropped on Japan at the end of World War II made it devastatingly clear to each and everyone of what great significance this relation is, and these events will certainly have enhanced its popularity enormously.
In short: the famous $E=mc^2$ was not popularized by a single person, but it probably became so famous because (1) It was discovered by Einstein (2) It contains physics that speaks to the imagination of many, while retaining remarkable simplicity (in notation). If there is anyone more knowledgeable on this topic than me, please feel free to correct me or add further reasons to this answer.
