The Duke of Holstein was a title held by the rulers of the historical region of Holstein, located in present-day northern Germany. The title emerged in the late Middle Ages and was associated with the House of Schauenburg. Holstein was often contested between various powers, including the Danish crown and the Holy Roman Empire. The dukedom was divided into several territories, including Holstein-Gottorp and Holstein-Pinneberg. The dukes played a significant role in regional politics and alliances, influencing the history of northern Europe. The title eventually became obsolete in the 19th century as the region underwent political changes.