Who was he?
Was born sometimes in the decade after 1243 and was killed in 1272 November. He was ofc a royal descent.
He was a relative of the Árpád dynasty via his mother, Anna, who was the daughter of king Béla IV.
His father was Rostislav from the Rurikids who himself had a very action packed life.
Rostislav was the prince of Halych (the III. with that name), Novgorod, Lutsk, and Chernigov. Then after he lost everything but the claim - thanks to his father-in-law, king Béla - Ban of Slavonia, then Duke of Macsó. Later he could form some claim to the Bulgarian throne, he was backed by both king Béla and his son István V but at that time the tzardom was contested by many claimants and his death prevented further ambitions. His lands (Macsó and Bosznia) were divided between his sons, and with the death of the older, Michael, the younger, Béla, united them again.
As an administrative unit in our Kingdom those lands served as defense for the frontiers and a staging area for southern campaigns. Three rivers posed as it's borders: in the west the Drina, north the Sava, east the Kolubara. The southern limits always changed with the ever changing situation. Those who ruled of these lands were one of the key figures in Hungary's politics and military, it isn't a wonder he played important parts in certain events which then led to his death.