This dissertation traces the responses of three canonical political realists-Niccolò Machiavelli, Thomas Hobbes, and Hans Morgenthau-to eruptions of apocalyptic rhetoric, imagery, and politics. I treat apocalypticism as a very particular kind of utopianism that is premised on a belief in the imminent end of the known world and the arrival of a radically new future. Contemporary realists tend to position their pragmatic approaches to politics against 'utopian' alternatives, which they reject for being at best unrealizable and at worst profoundly dangerous. However, in tracing the historical engagement between political realism and apocalypticism, I find a more complex and productive relationship. Through an historical and textual analysis of the work of Machiavelli, Hobbes, and Morgenthau, I argue that much of the nuance and texture in these realists' work, and particularly their evolving conceptions of human nature and their commitments to political action, emerge from serious and extended engagements with apocalypticism. ii