Hermann II, Count of Cilli

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 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 the Croatian lands. He served 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. Hermann was the most important representative of the line of Celje counts, having brought the family from merely local importance to the focus of Central European politics.

Hermann II was the younger son of Count Hermann I of Celje and his wife, Catherine of Bosnia. The House of Celje were Styrian vassals of the Habsburg dukes of Styria and Carinthia with estates along the river Savinja, in present-day Slovenia. Hermann's mother was a member of the House of Kotromanić, daughter of Ban Stephen II of Bosnia and thus cousin of the first King of Bosnia, Tvrtko I. His older brother Hans (c. 1363–1372) having predeceased their father, Hermann was the sole heir of their father upon the latter's death on 21 March 1385. The death of his son-less cousin William on 19 September 1392 made him the sole possessor of the family titles and estates.

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