Béla IV of Hungary

Béla was crowned in 1214 at eight years old over his father Andrew II's objections, then spent years governing frontier provinces - Slavonia, Croatia, Transylvania - where he courted Cuman chieftains and took the title King of Cumania in 1233. He inherited the throne in 1235 and immediately moved to reclaim royal lands his father had given away, alienating nobles and clergy. That tension became irrelevant on 11 April 1241, when Mongol forces annihilated his army at Mohi and chased him town to town until he reached Trogir on the coast. The Mongols withdrew in March 1242, leaving Hungary depopulated and ruined. Béla responded by decentralizing power - letting barons build stone castles and raise private armies, encouraging fortified towns, and welcoming thousands of colonists from Poland and the Holy Roman Empire. He built alliances eastward, briefly seized Styria, and expanded a buffer zone south through Bosnia and Serbia. In his final years he fractured his own kingdom, forced by dynastic conflict to cede everything east of the Danube to his son Stephen in 1266. He died in 1270 as a Franciscan tertiary; three of his daughters were later venerated as saints.