Vytautas the Great (Lithuanian: '; ; Ruthenian: "Vitovt"; Latin: "Alexander Vitoldus"; ca. 1350 - October 27 1430), also known in English by the traditional Polish and German name Witold"', was one of the most famous rulers of medieval Lithuania. With the title "Didysis Kunigaikštis", the equivalent of king, he was the supreme ruler of his dominions. The later translation is Grand Duke (for its etymology, see Grand Prince). Wikipedia
The definitive Wikipedia entry for Vytautas The Great. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Vytautas_the_Great