The Duke of Courland was a title held by the rulers of the Duchy of Courland and Semigallia, a historical region located in present-day Latvia. This duchy existed from the early 16th century until the late 18th century and was known for its relative autonomy within the Polish-Lithuanian Commonwealth. The dukes played a significant role in regional politics and trade, particularly in the Baltic Sea area. The most notable Duke of Courland was Jakob Kettler, who ruled from 1642 to 1682. Under his leadership, the duchy expanded its influence and established colonies, including a brief settlement in Tobago. The title of Duke of Courland became obsolete in the late 18th century when the region was absorbed into the Russian Empire.