Rostislav Mikhailovich
"Rostislav Mikhailovich (Hungarian: Rosztyiszláv, Bulgarian and Russian: Ростислав Михайлович) (after 1210 / c. 1225 – 1262) was a Rus´ prince (a member of the Rurik dynasty), and a dignitary in the Kingdom of Hungary.
He was prince of Novgorod (1230), of Halych (1236–1237, 1241–1242), of Lutsk (1240), and of Chernigov (1241–1242). When he could not strengthen his rule in Halych, he went to the court of King Béla IV of Hungary, and married the king´s daughter, Anna.
He was the Ban of Slavonia (1247–1248), and later he became the first Duke of Macsó (after 1248–1262), and thus he governed the southern parts of the kingdom. In 1257, he occupied Vidin and thenceforward he styled himself Tsar of Bulgaria.
" - (Wikipedia (en) 28.10.2019)