Peter Friedrich Wilhelm, Duke of Oldenburg[citation needed] (3 January 1754 in Eutin Castle, Eutin[citation needed] – 2 July 1823 in Schloss Plön, Plön.
[citation needed]) was a ruling Duke of Oldenburg from 1784 to his death.
Wilhelm was the son of Frederick Augustus I, Duke of Oldenburg and Princess Ulrike Friederike Wilhelmine of Hesse-Kassel.
[citation needed] Due to mental illness, Wilhelm was duke in name only, with his cousin Peter, Prince-Bishop of Lübeck, acting as regent throughout his entire reign.
She described the meeting between them in her famous journal: In a letter to her sister-in-law Sophia Albertina of Sweden, she described his condition: His title became Grand Duke in 1815, but Wilhelm never used the elevated style.