William J. Tonesk, born Władysław Jan Toniecki, served in several agencies of the United States intelligence community for three decades after World War II. These included: Office of Naval Intelligence, Special Services Unit, and Central Intelligence Agency; he also performed intelligence‑related duties within the Department of State. Most of his assignments were related to Polish matters and involved working with Poles. This article deals with the reasons that forced Tonesk to resign from the CIA, pondering the question whether his ethnic origin could have played a role. What enabled his career was his proficiency in the Polish language, command of other European languages, and experience and cultural immersion in the region. His first security slip prompted an internal investigation of his loyalty, and the nature of contacts with his Polish assets was questioned. However, the incident did not end Tonesk’s career in intelligence. This historical account maintains its relevance in today’s studies on diversity within US government, as Tonesk’s case study provokes new research questions concerning ethnic hiring by US intelligence.