Almost everyone has heard of e=mc the formula behind the Theory of Special Relativity - but very few people realise that it was just one of Einstein's significant scientific breakthroughs of the year. It might also be worth considering that this was just four years after the death of Queen Victoria. Few people would think of Einstein as being an eminent Victorian but in fact he was.
The first scientific paper that Einstein published in this year was on the photoelectric effect. It showed that light sometimes behaves like a stream of particles with discrete energies called "quanta" and sometimes behaves like a wave of energy. The paper earned him a Nobel Prize.
The second paper was on Brownian motion - a random motion that can be observed when very light particles (such as Indian ink) are suspended in a liquid (such as water). It is caused when the molecules of the liquid collide with the particles and propel them in different directions. The paper included an experimental test for the theory of heat.
The third paper was the most famous - the Theory of Special Relativity - that included the famous equation quoted above. Behind the equation is the idea that mass and energy are actually two versions of the same thing and the amount of energy contained in mass is related to a constant (c). And the other key idea is that space and time are related.