Critics of Shakespeare's Richard III have had difficulty explaining and validating the perennial engagement of theater audiences with Richard, a figure who violates the norms of morality and aesthetics by triumphantly asserting his own malevolence and taking narcissistic pride in his ugliness. This article analyzes Richard's problematic appeal by focusing on the play's use of "sinister aesthetics": in other words, a set of cultural conventions governing the representation of evil, which valorize the dark and hideous as admirable poetic subjects and, by association, risk encouraging the very values they label as evil. The play thereby affirms a poetics in which Richard is attractive and powerful because he is evil—and even because he is ugly. This analytical approach enables us to appreciate the full range of moral and aesthetic appeals available to Shakespeare and his audiences. It also elucidates the complex play of conflicting moral and aesthetic ideas that gives Richard III its poetic energy. Richard combines two sets of sinister conventions, a poetics of malevolent theatricality and a poetics of deformity, which the play uses to explore the tension between aesthetics and ethics that plagued Renaissance moralists. As a critical concept, sinister aesthetics can be applied more broadly to facilitate the analysis of artistic representations whose appeal runs counter to normative aesthetic standards.