Kernel
Von Neumann is the figure who contributed first-rate work to seven distinct disciplines in three decades. Pure mathematics, quantum mechanics, game theory, computer architecture, nuclear weapons, weather modeling, and the theory of self-replicating automata each carry his foundational papers.
Contribution
Stored-program computer architecture (1945 EDVAC report) — the basis of essentially every general-purpose computer since. Operator-theoretic foundations of quantum mechanics (1932). The 1944 Theory of Games with Morgenstern. The Manhattan Project implosion-lens design. Cellular automata as a substrate for self-replicating systems.
Civilization-scale significance
If a single figure's intellectual output explains postwar American technical supremacy, it is von Neumann. The architecture of every laptop, the framework of every game-theoretic policy debate, and the seed of every cellular-automaton-based simulation runs through him.