The study details the life and work of a nearly forgotten personality in the Hungarian minority history of Slovakia, Ödön Tarján. His contemporaries considered him not only an opposition politician who criticized the government minority and economic policies in the Czechoslovak republic (1918 – 1938), but also an agent of the Hungarian government. He was an outstanding economic expert and an éminence grise of the Hungarian parties who had substantial influence on the administration in Budapest. Despite his Jewish descent, he claimed to belong to the Hungarian national minority. Tarján's career can be considered successful until around 1933. He was owner and manager of an industrial enterprise that was prosperous until 1918, though, later the company had difficulties with marketing and struggled financially. Tarján was an active freemason and gained significant influence in the minority policy during the 1920s. He maintained strong connections with the government in Budapest through collaboration with József Szent-Iványi, the chairman of the Hungarian National Party and developed important contacts within the Czech and Slovak industrial circles. Tarján's career took a downward turn in 1933 when he moved to Hungary. From then on his life was affected by existential difficulties and included many compromises. Although he was an expert on Czech-Slovak issues during the Hungarian revisionist movement, he moved to the periphery of political life there. Tarján died tragically in 1946.