Abstract: This Article is dedicated to retiring the now-dominant "rational actor" model of human agency, together with its numerous "dispositionist" cohorts, and replacing them with a new conception of human agency that the authors call the "situational character." This is a key installment of a larger project recently introduced in an article titled The Situation: An Introduction to the Situational Character, Critical Realism, Power Economics, and Deep Capture, 152 U. Pa. L. Rev. 129 (2003). That introductory article adumbrated, often in broad stroke, the central premises and some basic conclusions of a new approach to legal theory and policy analysis. This Article provides a more complete version of one of those central premises by elucidating a more realistic conception of the human animal than is currently embraced in legal theory. The Article begins with a short introduction to the larger project, and describes the central place that a realist conception of the human actor plays in that project. It then explores several bodies of literature within the fields of social, cognitive, behavioral, and neural psychology in pursuit of a vision of the human actor that is grounded in social science. Having explicated that conception, the Article then outlines some of the basic implications of it for law, legal theory, and social policy. It then analyzes conventional legal scholars', particularly legal economists', arguments for ignoring the lessons of social science in their treatment of human agency. As part of that analysis, this Article describes why recent efforts to incorporate some psychological findings - the sort of work that is often labeled "behavioralist" - have been inadequate. Finally, the authors briefly look beyond the human actor itself to consider some of the fairly obvious - but generally ignored - realities of our present social situation, and some of their implications for common policy presumptions. As subsequent work will make clear, this new, situationist conception of the human animal is as important to a realist account of law and legal theory as the dispositionist conception has been to now-dominant accounts.