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.