Terrorism is routinely portrayed in the twenty first century as an evil perpetrated by Arab/Muslim barbarians—Evildoers—waging a holy war against the Western civilisation. This study challenges not just this present understanding of terrorism, but the very existence of a ding an sich of terrorism. Using a combination of Foucault’s archaeological and genealogical methods it provides an alternative history of the phenomenon in the form of a history of its discursive structuring: the regimes of practices that governed what could and could not be thought of, identified, defined, known, judged and punished as ‘terrorism’ during particular epochs, and particular places. It asserts that the conceptual anchor point of the present Evildoer-terrorist is the rebel who opposes established order, and identifies the first such figure in modern Western history as the Devil who rebelled against God and came to play a significant politico religious role in Western societies of the Middle Ages. The discourse of ‘terrorism’ emerged from the epistemic spaces created from the separation of religion and politics in the eighteenth century, from when onwards rebellion was no longer a sin but a crime. Since then, various other rebels have been brought under the domain of terrorism during different epochs, the latest of whom is the Evildoer. This is not to say that the Devil remained a blatant constant in the forefront of Western terrorism discourse, but that the various rebels share a conceptual history that made it possible for the contemporary terrorist to be the Evildoer that he is. How the rebels came to be known as terrorists during various epochs and the various mechanisms implemented to defend societies against them, it is argued, are irrevocably linked: one could not exist without the other. The contemporary terrorist cannot be known as an Evildoer without the War on Terror; at the same time, the War on Terror cannot be waged without the knowledge of the terrorist as an Evildoer. To demonstrate this power/knowledge dyad at work, this study analyses what was said and done about terrorism by the United States and the United Kingdom, the foremost allies in the War on Terror, during its first ten years. In the differences in their discourses emerges not just the ontological uncertainty of terrorism but also how these mechanisms for establishing the ‘truth’ of terrorism function as mechanisms of power. It is asserted that the Evildoer has made possible, and was made possible by, some of the most significant changes in how power is exercised in Western societies since the separation of religion and politics in the eighteenth century.