This paper offers a conceptual analysis of charismatic leadership, beginning with the observation that such phenomenon is often portrayed as irrational, disruptive and individualistic. As it is not unusual for debates in sociology to be presented in terms of dichotomous logic, the issue might be framed in terms of 'agency versus structure' and 'reason versus emotion', where emotion and agency are pitted against rationality and civility. Weber's work on charismatic authority demands an understanding of these categories and of his methodology; this paper briefly establishes a degree of ambivalence in the approaches of the received scholarship in relation to these themes. I argue that the charismatic leader is neither an 'irrational Superman' nor the inevitable expression of forces of social change, but a rational crucial instrument in the transient process of political change and subsequent social transformation. The rest of the paper illustrates some aspects of this process with reference to the rise of Juan Per㮠in Argentina. The relation between agency and structure or between the charismatic leader and the systems that constitute society is shown to be interactive, fluid and immediate, accompanied by the destruction and reconstruction of institutions in the rational pursuit of a new social order.