The origins of graph theory are humble, even frivolous … The problems which led to the development of graph theory were often little more than puzzles, designed to test the ingenuity rather than the stimulate the imagination. But despite the apparent triviality of such puzzles, they captured the interest of mathematicians, with the result that graph theory has become a subject rich in theoretical results of a surprising variety and depth.
Leonard Euler, about the Königsberg Bridge Problem, origin of Graph Theory
