Stjepan Vukčić Kosača

Stjepan Vukčić Kosača, Grand Duke of Bosnia and Duke of Saint Sava, was the most powerful nobleman in the Kingdom of Bosnia in his time. A member of the Kosača noble family, he became Grand Duke of Bosnia upon the death of his uncle Sandalj. He refused to recognize the accession of King Tomaš, throwing the kingdom into civil war. During this time he took the opportunity and titled himself a herzog, and while reaching for assistance, he aligned himself first with the Ottoman Empire, then Aragon and again the Ottoman Empire. Peace was restored by the marriage of King Tomaš and Stjepan's daughter Katarina, but it did not last long. However, with a death of king Tomaš and ascension of his son and heir, Stjepan Tomašević, to the Bosnian throne peace was finally achieved for the kingdom.