Biographical medailon of the excellent and most famous Czech Byzantinist, professor of Charles University and later also of Harvard University msgre Francis Dvorník. Three major research topics he studied in the subsequent periods of his academic career are examined: his epoch-making monographs on the Christianization of the Slavs from Byzantium and, in particular, on the Cyrillo-Methodian mission written during his postgraduate studies in Paris and the following academic career in Prague, his revolutionary book on the Photian schism completed during his exile in England in the time of World War II, and his monumental work on the Early Christian and Byzantine political philosophy that he produced at Dumbarton Oaks Center for Byzantine Studies in Washington, DC. Besides his scientific work political activities of Professor Dvorník are described too, whether it was his co-operation with the Czechoslovak ministry of foreign affaires in the time between the wars or his support of various Czech cultural institutions in exile when he later lived in the US.