Since the second half of the 20th century, rational choice theory (RCT) has gained extraordinary prominence in economics and records a history of powerful applications across the social sciences. Disunity however exists among defenders and opponents alike with respect to its nature, status and role in actual practice. This disunity has given rise to fundamental disagreements about the theory’s epistemic potentials and limitations and has fueled charges against the economics profession of imperializing the social sciences. I develop a narrative that contributes to an explanation for this disunity and partly alleviates the accusations of ‘economics imperialism’. By tracing the historical emergence of RCT in American economics from the 1940s to the 1970s, I argue that its development was fundamentally shaped by different disciplinary orientations and by the prevalence of diverging epistemic interests. On the one hand, RCT was developed to serve as a theory of individual decision-making in the behavioral sciences and as a contribution to a ‘representational theory of measurement’. This proved to be especially of interest for the development of ‘scientific psychology’ and the project of operationalizing individual values. On the other hand, RCT was developed into a behavioral foundation within the formal-logical construct of general equilibrium theory in mathematical economics. Given its different manifestations, it appears fruitful to understand RCT as a highly flexible set of problem-solving tools used for fundamentally distinct purposes, rather than in terms of a unified theory of individual behavior. Contrary to alternative narratives that proclaim economics imperialism, I furthermore argue that the history of RCT reveals a ‘rational choice imperialism’ that has had an impact on the economics profession comparable to its effects on other social scientific disciplines. In order to support the argument, my analysis is largely placed within the context of Jacob Marschak’s theoretical contributions to RCT and his professional biography.