What is the overall name for a branch of applied mathematics used to study behaviour in strategic situations, in which an individual's success in making choices depends on the choices of others?

What branch of mathematics was founded from a paper "On a Characteristic Property of All Real Algebraic Numbers" (1874) by Georg Cantor, who built on the work of Zeno, Bernard Bolzano & Richard Dedekind, which, in turn was followed up by Bertrand Russell, Ernst Zermelo, Abraham Fraenkel & Henri Lebesgue?