John von Neumann

1. Von Neumann Entropy

Extension of classical entropy to quantum mechanics.

$$ S(\rho) = -\text{Tr}(\rho \ln \rho) $$

2. Minimax Theorem

The foundation of game theory.

$$ \max_x \min_y v(x, y) = \min_y \max_x v(x, y) $$