Pirates are commonly referred to as hostis humani generis, the enemy of all. This essay explores the contours of this figuration through an analysis of early nineteenth century American legal and political texts concerning piracy. I argue that pirate rhetorics in this period are part of a constitutive rhetoric of sovereignty, principally identified with Emerich de Vattel’s famous definition of sovereignty in The Law of Nations. Through an analysis of the textual milieu surrounding the U.S. Supreme Court’s 1820 decision in United States v. Smith, I show that the pirate is figured as an anti-sovereign, which allows for the consolidation of an otherwise differential system of international relations characterized by liberal, self-interested, sovereign nations. In becoming hostis humani generis, the pirate enters into an antagonistic relationship with the sovereign that provides the ontological ground for the theory of sovereignty characteristic of modern thought in international law. Supplementing Charland’s theory of constitutive rhetoric with Laclau and Mouffe’s work on antagonisms in social relations, I argue that focusing on negative identification, which is an essential component of any constitutive rhetoric, opens up unique avenues for analysis that may otherwise be obscured by attending solely to the positive dimensions of a rhetoric.