Peter Friedrich Wilhelm, Duke of Oldenburg, (3 January 1754, Eutin Castle

Eutin Castle

Eutin Castle in Eutin in the north German district of Ostholstein is the cultural centre and nucleus of the town and, together with Gottorf and Glücksburg Castles, belongs to the most important courtly secular buildings in the state of Schleswig-Holstein....

, Eutin

Eutin

Eutin is the district capital of Eastern Holstein located in the northern German state of Schleswig-Holstein. As of 2005, it had some 17,000 inhabitants....

 – 2 July 1823, Schloss Plön, Plön

Plön

Plön is the district seat of the Plön district in Schleswig-Holstein, Germany, and has about 13,000 inhabitants. It lies right on the shores of Schleswig-Holstein's biggest lake, the Great Plön Lake, as well as on several smaller lakes, touching the town on virtually all sides...

.) Wilhelm succeeded his father, Frederick Augustus I, Duke of Oldenburg

Frederick August I, Duke of Oldenburg

Friedrich August, Duke of Holstein-Oldenburg was the son of Christian August, Duke of Holstein-Gottorp and his wife Margravine Albertine Friederike of Baden-Durlach.-Marriage and issue:...

 as the Duke of Oldenburg in 1785. Wilhelm's mother was Princess Ulrike Friederike Wilhelmine of Hesse-Kassel

Princess Ulrike Friederike Wilhelmine of Hesse-Kassel

Princess Ulrike Friederike Wilhelmine of Hesse-Kassel was a member of the House of Hesse-Kassel by birth, and of the House of Holstein-Gottorp through her marriage to Frederick Augustus I, Duke of Oldenburg...

.

The title became a Grand Duke

Grand duchy

A grand duchy, sometimes referred to as a grand dukedom, is a territory whose head of state is a monarch, either a grand duke or grand duchess.Today Luxembourg is the only remaining grand duchy...

 in 1815, but Wilhelm never used the elevated style. It was not used until 1829 by the son of Wilhelm's cousin and successor, Peter I. http://www.btinternet.com/~allan_raymond/Oldenburg_Royal_Family.htm