Oldenburg

The House of Oldenburg takes its name from Oldenburg Castle on the Hunte in Westphalia. Its first historical ancestor, Huno of Rustringen, founded Rastede monastery in 1059; Count Elimar I is documented from 1091. Vassals of the Saxon dukes, the counts became imperial princes when Emperor Frederick I dismembered Saxony in 1189.

In 1423 Theodoric of Oldenburg married Hedwig of Holstein, heiress of Scandinavian royal blood. Their son Christian was elected King of Denmark in 1448, Norway in 1450 and Sweden in 1457, ruling the Kalmar Union. He left the county to his brother Gerhard; the comital line ended in 1667, after which Denmark ruled Oldenburg.

The Holstein-Gottorp branch, founded in 1544, supplied Swedish kings from 1751 and the Russian tsar Peter III in 1762. Denmark ceded Oldenburg to it in 1773; Oldenburg became a duchy in 1774 and a grand duchy in 1815.