Prototypes have long been acknowledged as playing a critical role in the emergence and consolidation of new organizational and market categories. However, the precise forms, characteristics, and effects of prototypes in the categorization process remain unclear. We address this gap by conducting a discourse analysis of different stakeholder contributions to the emergence of the new legal category of 'modern slavery' in the context of the UK's Modern Slavery Act, 2015. Drawing on a political agency view of categorization, our findings reveal that contrary to existing research, the role of prototypes in categorization is heterogeneous. Our analysis identifies four different general forms of prototype, namely typifying, mobilizing, familiarizing, and scoping prototypes, each of which are deployed by different actors to achieve specific goals in the emergence and consolidation of the new category.