I've heard that cracking the Enigma Code shortened the war by 2 years and saved 14 million lives, how is such an estimate made? And, what else did he do apart from cracking the Enigma Code?
A couple years back /u/k1990 wrote a detailed reply describing the origin of this estimate and the perils of conjecturing about alternative timelines with additional comments from /u/restricteddata.
I will (preteritively) let someone else detail his work in the theoretical limits of computation and early thoughts about artificial intelligence.