John Nash was a mathematician whose genius for game theory transformed economics, biology, and military strategy. At age 21, he wrote a 28-page dissertation introducing the 'Nash Equilibrium'—a situation in a competitive game where no player can benefit by changing their strategy if the other players keep theirs unchanged. This concept provided a mathematical way to understand complex decision-making in everything from nuclear standoffs to corporate negotiations. Nash’s life was also marked by a long struggle with schizophrenia, a story popularized in the film 'A Beautiful Mind.' He eventually recovered and was awarded the Nobel Prize in Economics in 1994, followed by the Abel Prize in mathematics in 2015.