Founder identity plays an important role in entrepreneurship, affecting core strategic decisions. Drawing on social identity theory (Tajfel & Turner, 1979; Tajfel, 1981) and social categorization theory (Turner et al, 1987) the burgeoning literature on founder identity mainly focuses on in-groups and affirmational categorization, raising the fundamental question “Who am I?” (e.g. Fauchart & Gruber, 2011; Powell & Baker, 2014). In this paper we emphasize out-groups and negational categorization trying to answer the question “Who am I Not?” We propose that the dual perspective of affirmational and negational categorizations provides a more nuanced picture of the founder’s distinct self-concepts, and enhances our understanding as to why differences in firm creation processes and outcomes exist.