Hermann II (Slovene: Herman; early 1360s – 13 October 1435), Count of Celje, was a Styrian nobleman and magnate, most notable as the faithful supporter and father-in-law of the Hungarian king and Holy Roman Emperor Sigismund of Luxembourg. Hermann's loyalty to the King ensured him generous grants of land and privileges that led him to become the greatest landowner in Slavonia. He served as governor of Carniola, and twice as ban of the combined provinces of Slavonia, Croatia and Dalmatia, and was recognized by a treaty in 1427 as heir presumptive to the Kingdom of Bosnia. The House of Celje's rise to power culminated in achieving the dignity of Prince of the Holy Roman Empire. At the peak of his power, he controlled two thirds of the land in Carniola, most of Lower Styria, and exercised pow