John F. Nash Jr. is widely known as the subject of the Oscar-winning film “A Beautiful Mind,” but his contributions to the advancement of human knowledge are far greater. Nash paved the way for game theory to spread from a collection of toy cases in mathematics to a generalizable theory applicable to virtually anything — board games, economics, politics, international relations — to the point where now it’s practically a mode of critical thinking in its own right. On Saturday, the 86-year-old mathematician and his wife, Alicia, were killed in a car crash in New Jersey. There have been...