In this article I consider the significance of the New World African slave to Marx's Capital. Although Marx frequently refers to slaves, the products of slave labor, and events centered on slavery like the American Civil War, and although he deploys the rhetoric of enslavement to describe the exploitation of wage laborers, he never acknowledges the slave as essential to his analysis. This is because Marx, for the sake of his analysis, accepts the widely held view in the nineteenth century that slaves lacked agency. I argue for the necessity of the slave to Capital, demonstrate how taking this seriously alters some key concepts in Capital, and re-read Marx so that the slave's agency can be traced from within Marx's theoretical apparatus.