King of the Slavs (Latin: rex Sclavorum, Sclavorum rex) was a title denoting some Slavic rulers, as well as Germanic rulers that conquered Slavs, in the Middle Ages in European sources, such as Papal correspondence.
^Concise Dictionary of Proper Names and Notable Matters in the Works of Dante. Ardent Media. 1968. pp. 566–. GGKEY:P53U8KC8WZR. Addressed (in 1288) by Pope Nicholas IV as 'Rex Sclavorum'; he signed himself (in 1305 or 1307) in a document still extant in the Venetian archives as ' Stephanus Urosch Rex Serbicarum terrarum et maritimarum '. a [Stefano Urosio.] ...