Peter I or Peter Frederick Louis of Holstein-Gottorp (German: Peter Friedrich Ludwig von Holstein-Gottorp) (17 January 1755 – 21 May 1829) was the Regent of the Duchy of Oldenburg for his incapacitated cousin William I from 1785 to 1823, and then served himself as Duke from 1823-1829. He also served from 1785 to 1803 as the last Lutheran Prince-Bishop of Lübeck, until that Prince-Bishopric was secularized and joined to Oldenburg. Peter Frederick Louis was born on 17 January 1755 at Riesenburg. He was the only surviving son of Prince Georg Ludwig of Holstein-Gottorp and Sophie Charlotte of Schleswig-Holstein-Sonderburg-Beck. On 6 June 1781, he married Duchess Frederica of Württemberg, the second daughter of Frederick II Eugene, Duke of Württemberg and his wife, Friederike Dorothea of Brandenburg-Schwedt. Frederica's sister, Sophie, was the wife of Crown Prince Paul of Russia (the future Tsar Paul I. Peter and Frederica became the parents of two sons: August (born in 1783) and George (born in 1784). He was appointed Regent of the Duchy of Oldenburg for his incapacitated cousin Peter Frederick William in 1785. From 1785 until 1803, he also served as the last Lutheran Prince-Bishop of Lübeck, until that Prince-Bishopric was secularized as the Principality of Lübeck and joined to Oldenburg. Following the death of Wilhelm in 1823, he himself became reigning Duke of Oldenburg. Although the Duchy of Oldenburg had been elevated to a Grand Duchy in 1815, he refrained from using the title of Grand Duke. His son, Augustus, was the first Duke of Oldenburg to use the style of Grand Duke. Peter I died on 21 May 1829 in Wiesbaden. He was buried in the Ducal Mausoleum in the Churchyard of Saint Gertrude in Oldenburg.

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