Game, set, and graph

In the twentieth century the theory of games was transformed. It began as an amusing pastime, and ended as a major branch of mathematical research and a key paradigm of economic theory. Here it will be argued that the transformation was the result of the work of mathematicians, such as Ernst Zermelo, John von Neumann and Dénes Kőnig, who also contributed to two other areas of mathematics that were emerging at the same time: the theory of sets and the theory of graphs.