The Duke of Schleswig is a historical title associated with the region of Schleswig, located in present-day Denmark and Germany. The title emerged in the Middle Ages and was held by various noble families, often linked to the Duchy of Schleswig. The area has a complex history, marked by territorial disputes and shifting allegiances between Denmark and Germany. The title became particularly significant during the 19th century, especially during the Danish-German War of 1864. Following the war, the Duchy of Schleswig was annexed by Prussia, leading to the dissolution of the ducal title's political power. Today, the title is largely ceremonial and of historical interest.