This dissertation examines the career of Horace Newton Allen, an American physician who became the first Protestant missionary to reside in Choson Korea. It focuses specifically on the initial decade of his tenure on the peninsula (1884-1894), the period when he transitioned from a participant of the Protestant foreign mission movement to a member of the American diplomatic service. These years also comprised the formative era of relations between the United States and Korea. Through a close look at Allen's work and activities, this study uses his story as window into the broader dynamics of the early American-Korean encounter. In particular, it challenges previous characterizations of Horace Allen as an exemplar of US expansionism, and argues instead that his career was shaped in large part by the divergence in American interests vis-à-vis Korea during the late nineteenth century.