Béla IV (1206-1270) was the king of Hungary between 1235 and 1270.

Bela was the son of Andrew II and Gertrude of Meran. His mother was murdered by Hungarian magnates when he was a boy. In 1218 he was married to Maria Laskarina, the daughter of Emperor Theodore I Lascaris Nicaea. Their children were:

1. Kinga, married King Boleslaus V of Poland
2. King Stephen V of Hungary
3. Erzsébet, married Duke Henry XIII of Lower Bavaria

In 1238, Hungary was invaded by Kuman tribes fleeing the advancing Mongol hordes. Bela sought to ally with the Kumans, and so he granted them asylum and betrothed his son and heir Stephen to the daughter of a Kuman khan named Kuthen. The Kumans (originally a pagan shamanist people) converted to Christianity and were baptised. They fought beside the Hungarians against the Mongols.

Bela tried with little success to reestablish royal preeminence by reacquiring lost crown lands. His efforts, however, created a deep rift between the crown and the magnates just as the Mongols were sweeping westward across Russia toward Europe. Aware of the danger, Bela ordered the magnates and lesser nobles to mobilize. Few responded, and the Mongols routed Bela's army at Mohi on April 11, 1241. His ally Kuthen had been killed by mistrustful Hungarian lords in Pest just prior to the invasion.

Bela fled first to Austria, where Duke Frederick of Babenberg held him for ransom, then to Dalmatia. The Mongols reduced Hungary's towns and villages to ashes and slaughtered half the population before news arrived in 1242 that the Great Ögedei Khan had died in Karakorum. The Mongols withdrew, sparing Bela and what remained of his kingdom.

Her daughter, Margaret (Margit) (1242–1270) mostly lived on Margaret Island, which was later named after her. She was canonized in 1943.