In lieu of any attempt to write a sweeping, general account of ‘classical’ security studies or realist thought, I propose to investigate the ethical positions taken by a theorist synonymous with both, Hans J. Morgenthau. 1 Despite the still widespread misrepresentation of Morgenthau as an amoral theorist of international relations (IR) or as only minimally interested in ethics, the ‘father’ of Realism in IR was very clear regarding the importance of ethics in his analyses of international law and international politics: ‘The guiding influence. . . as to the ideals, ends, and interests to be pursued by the norms under which a given society lives, emanates from the ethical sphere.’ 2 In the course of the chapter, I examine two distinct but linked aspects of Morgenthau’s ethical theory: his political-sociological critique of the foundations of post-World War One international society, and his wider, post-1945 project to ground an ethics of the lesser evil firmly within a political framework predicated upon power and necessity.