This article analyzes the perception of Kaiser Wilhelm II by the British foreign policy elite from the mid-1880s to 1914. Drawing on regular diplomatic reporting by Britain's representatives abroad as well as a wide range of private papers, it examines a series of seemingly minor incidents, which nevertheless played a significant role in shaping British establishment views of the last German Emperor. One of the key elements of British elite perceptions was the Kaiser's assumed, rumoured, and frequently commented-upon mental instability. The article seeks to demonstrate that Wilhelm's idiosyncrasies were of greater significance in the formulation of British policy towards Germany than has been previously acknowledged. British concerns about the Kaiser's flawed personality did not arise sporadically in response to his better known "outbursts" but were constantly present. As such they did not simply mirror the manifold problems with which Anglo-German relations were increasingly fraught after the turn of the century. On the contrary, the Kaiser's perceived public and private persona was one of these problems.