I'd like to be a fly on the wall when Hannibal Barca, Alexander the Great, Genghis Kahn, and Bai Qi discussed war and empire building.
Babbage/Lovelace, Turing, Al Kwarzemi, Dennis Richie.
Damn, only four makes the setup difficult. I also had Grace Hopper and Konrad Zuse on the shortlist. Just the WW2 contributors would be another combo that would be amazing.