I wouldn't credit Kalashnikov quite so highly, the real key was the invention and wide post-WWII adoption of non-corrosive primers, which radically decreased the maintenance required after firing a gun. After that, it was the Soviet system that ensured zillions of reliable, low/no maintenance weapons would flood the world; Kalashnikov's was the later, but it was proceeded by the SKS (same round, fixed magazine fed by clips).
But using him to represent all the of the above works. I'd add John Moses Browning, history's greatest and most influential small arms designer, if for no other reason a design detail that's used in almost every semi-auto pistol today. And we are still using weapons he designed in the 1910s, e.g. the 1918 M2 heavy machine gun and the M1911 handgun, one of which I carry almost every time I walk out my door.
I'd add Jay Forrester, who's Project Whirlwind invented the physical computer as we know it; he left the field after that project, saying correctly all the really important and interesting stuff had been accomplished.
Alfred Nobel, inventor of the first stable high explosive (stabilized nitroglycerin known as dynamite).
Pick a selection from Thirty Years That Shook Physics (quantum physics), and go back some, at least to Newton and Leibniz. And, oh, Euclid.
Claude Shannon is best known as the father of information theory, but before that he wrote one of the most consequential master's thesis ever, in which he applied Boolean logic to found both digital circuit and digital computer design.
Hewlett, Packard and Shockley unintentionally founded Silicon Valley.
John Ericsson, inventor of the monitor class of warships (http://en.wikipedia.org/wiki/Monitor_(warship) ) and how they influenced naval design following.
Tesla, for AC power, Edison's DC had strict transmission length limits.
Time for breakfast, that'll do for now.