Founder centrism refers to the ideological tendency in religious communities to treat the actions and ideas of religious founders as the most important, leading, and normative aspect of the community’s institutions, practices, and beliefs. Like all ideologies, founder centrism has a history that it seeks to conceal. Although scholars recognize that founder centrism is prevalent in Japanese Buddhism, it has received little sustained scholarly attention. As a prolegomenon to the deeper investigation of the history of founder centrism in Japanese Buddhism, this dissertation examines key developments during the early medieval period (ca. (eleventh through mid-fourteenth centuries CE). I conclude that the enduring preeminence of founder centrist perspectives in Japanese Buddhism traces not, as is frequently assumed, to the early modern era, but in part also to this earlier period. Put briefly, I show that the powerful monastic establishment of early medieval Japan assured its own reproduction over time in large part through the instrumentalization founder centric ideas. Founder centrism thus functioned, for them, as a kind of hegemonic ideology that solidified its dominant position and interests both in the Buddhist community and in society writ large. As such, the history of founder centrism in Japanese Buddhism is inextricably linked to the institutional politics of that medieval establishment. Aside from shedding further light on the complex histories of Buddhism in Japan, this dissertation seeks to contribute to an emergent trend in scholarship to examine not the historical founders of religions, but rather their subsequent discursive construction by later adherents of the communities.