By recounting the history of the racialization of the Rwandan identity categories of “Hutu” and “Tutsi”, whose political manipulations divided Rwanda throughout the twentieth century, this article shows the impact of racial ideology on the personal representations of the Rwandese. This is what historian José Kagabo has named: “The Triumph of the Idea”: a latent imaginary rooting biological data into a layer of representations, sometimes mutually negative between communities, and upon which the Tutsis’ genocide originated in 1994. This relationship to identities was, ruthlessly, to draw the line between executioners and victims.