Stjepan Vukčić Kosača

Stjepan Vukčić Kosača (1404–1466) was a powerful Bosnian nobleman who was politically active from 1435 to 1466; the last three decades of Bosnian medieval history. During this period, three kings acceded to the Bosnian throne: Tvrtko II, Thomas (Tomaš), Stephen Tomašević (Stjepan Tomašević) and anti-king Radivoj—the older brother of King Thomas—before the country was conquered by the Ottomans.

Stjepan, a son of the Knez of Drina, Vukac Hranić, and Katarina, whose ancestry is unknown, was probably born in 1404. Stjepan's father held hereditary lands in the Upper Drina region. Stjepan was a member of the Kosača noble family and became its chieftain in 1435 when he succeeded his uncle, Duke Sandalj, as Duke of Humska zemlja and the Grand Duke of Bosnia. Stjepan influenced the development of the late Bosnian medieval state more than any other person of his era.

Stjepan supported Radivoj in the line of succession for the Bosnian throne and refused to recognise the ascension of King Thomas, leading to a series of civil wars in the kingdom. During this time, Stjepan added the title herzog (Serbo-Croatian: herceg) to his intitulation. While searching for help, he aligned himself first with the Ottoman Empire then the Crown of Aragon, and again the Ottoman Empire. The marriage of King Thomas and Stjepan's daughter Katarina temporarily restored peace, but with the death of King Thomas and the ascension of his son and heir, Stephen Tomašević, to the Bosnian throne, peace was finally restored and reconciliation was achieved. This ensured the nobility's, including Herceg Stjepan's, full support of the king and loyalty for the kingdom, which was facing the Ottomans' advancement.

It was Stjepan's herceg title that gave rise to the name of Herzegovina (Serbo-Croatian: Hercegovina), which was used as early as 1 February 1454 in a letter Ottoman commander Esebeg wrote from Skopje. In 1470, Herzegovina was separated from the Sanjak of Bosnia and reorganised into the Sanjak of Herzegovina, with a seat in Foča. The name remains in use for the southernmost region of Bosnia and Herzegovina. The town of Herceg Novi in present-day Montenegro, which was founded by Tvrtko I of Bosnia as Sveti Stefan—the name that from the beginning gave way to a name Novi (literally "New"; also known as Castelnuovo in Italian, New Castle in English)—later came to Kosača possession and become their winter seat. During this era, the town was renamed again by adding Stjepan's title herceg (Serbo-Croatian pronunciation of German ''herzog'') to the name Novi, which gave it the current name of Herceg Novi.