The Dukes of Oldenburg were a noble family that ruled the Duchy of Oldenburg in northern Germany. Their lineage can be traced back to the 12th century, and they played a significant role in the region's history. The family produced several notable rulers and was influential in the politics of northern Europe. In the 19th century, the Dukes of Oldenburg expanded their influence through marriages and alliances, connecting with other royal families, including the House of Romanov in Russia. The last Duke, Peter II, ruled until the end of the monarchy in Germany after World War I, leading to the establishment of a republic.