What is morality’s place within realist theories of international politics? Often realism is disregarded for having little to offer on the matter. Whilst recent research suggests this is something of a misconception, seldom have realists themselves been asked if and where any moral philosophy belongs inside their perspectives, respectively, on world politics. This is probably unfair, and not a little strange, as several realists throughout the history of international political thought have in fact had much to say about what becomes of morality between states. This paper presents a small selection of those most important contributions to the realist literature, with a particular view towards what has been said on morality within them. Identified are a handful of instances where influential realists have indeed commented on what becomes of morality in international politics, with each example then taken to be useful in some way. Next is proposed something like a complement to them, by way of reading differently the origins of the classical realist tradition. This alternative reading requires first that we consider the ancient Greek sophist Protagoras as having had something important to say about morality and about human nature in Plato’s dialogue named after him. Second, we must ask whether Protagorean moral philosophy can at all be considered relevant to the development of realist theory. I argue that it can, and suggest that we ought therefore to revisit the realist tradition's ancient Greek origins, adding next to the name Thucydides that of his contemporary Protagoras as having been first to exemplify realist theory in the history of Western international political thought.