Theory of Games and Economic Behavior
Von Neumann and Morgenstern gave a formal apparatus for choosing an action when the outcome depends on another player.
Why it matters
Decision under conflict took a mathematical form that game search and move evaluation later relied on.
The book introduces zero-sum games, the minimax solution and the utility function. It says nothing about computing machines, yet the minimax idea became the backbone of Shannon's chess paper a few years later and of every program that searches moves.