Marcus du Sautoy in The Guardian:
This year we are celebrating the centenary of the most famous equation of all time. Einstein’s E=mc2 is probably at the top of most people’s list of memorable equations. Like all great equations, Einstein’s discovery has the quality of a magic trick: you start with something on one side of the equation and then by mathematical magic the formula transforms it into something that appears completely different. In Einstein’s case, the trick was to show how matter (the m in his equation) can be transformed into pure energy (the E), a magic trick that was put to devastating use in the creation of the atom bomb.
More here.