It is usually claimed that Simon’s notion of bounded rationality has little to do with bounded rationality as today understood in behavioral economics. However, the fact that both terms – i.e. bounded rationality and behavioral economics – are original Simonian jargon suggests that later theorists of bounded rationality have chosen to stay on Simon’s shoulders, at least for rhetorical or instrumental reasons. This paper reconstructs the development of the notion of bounded rationality (and, to a lesser extent, of behavioral economics) through the lens of Simon’s point of view, first as founder and then as ‘Nobel father’ of bounded rationality. The main idea of the paper is that Simon did never aim to provide a unitary notion of bounded rationality. Rather, Simon proposed, from the beginning, a modular notion of bounded rationality, composed by conceptually complementary but independent modules, the cognition of individuals on the one hand and the environment to which they adapt on the other hand. Modularity is evident in the well-known publication path of the two foundational papers on bounded rationality, the one in a journal of economics, the other in a journal of psychology. I show that this modular publication strategy was driven by the peculiar features of the different disciplines: that is to say, Simon ‘modulated’ the arguments on the basis of what each discipline was more prone to listen as arguments in favor of bounded rationality. And, economics was more prone to listen to the module of ‘computational and information boundaries’ of human cognition than to the ‘environmental’ module. Through this lens, I reconstruct Simon’s relationships with early neoclassical opponents to bounded rationality, with Kahneman and Tversky, with later neoclassical theorists of bounded rationality in economics and, in the end, with supporters of ecological rationality. The emphasis on the ‘cognitive limitations’ module – the trademark of bounded rationality in economics – allowed Simon both to claim his imprinting on the later theories of bounded rationality and to be considered by them as the true forefather when needed. This reconstruction is here also supported by new archival material.