Nash's game theory dissertation was something von Neumann considered obvious and not particularly noteworthy, if I remember my lore right. He was among the first game theorists, focusing more on collaborative games than pure strategic/competitive games.
Einstein built on the shoulders of Riemann, Gauss, and others when considering the universe might be non-Euclidean!
All brilliant people, many singular minds of great repute, yet, all improved by the rest.
I believe Nash himself didn't consider it particularly noteworthy either, and was far prouder of his work in pure math (like the Nash embedding theorem).
another famous piece of Von Neumann lore is that he constantly advocated nuking the Soviets.
Saying that von Neumann was one of the first game theorists undersells it.
He wrote the original book on game theory! The Theory of Games and Economic Behavior with Oskar Morgenstern.
Relatedly, MAD was his conception as well.