The historiographical debate on Wilhelm II’s alleged personal rule and on his role in the 1914 decision to go to war generally neglects how the institution of the kaiser (the imperial office) evolved in the context of the federal state. In addressing this lack of research, this essay exposes fundamental developments of the imperial office in the federal legislature and executive between 1871 and 1918. It argues that under the 1871 constitution the power of the Emperor was based on Prussia, which, in turn, made him subject to federal constraints. In the legislature, the evolution of the imperial office was characterized by the emergence of the right to initiate legislation and to veto laws, which turned the Emperor into a material factor in legislation. In the executive, his constitutionally established dominance increased over the years, for example in terms of the expansion of his right to decree ordinances across all fields of government. At the same time, the other federal organs, especially the Reichstag, tried to curtail qualitatively the new appointment powers of the kaiser in order to limit Wilhelm II’s disruptive influence on the political system. The general expansion of the Emperor’s legislative and executive power, however, was due to systemic reasons of federal evolution rather than the persons in office. This evolution should prompt historians to reconsider the role of the kaiser in imperial politics by paying more attention to the federal context and, especially, by measuring his conduct by what the capacity of his office looked like in constitutional reality at the relevant moment.