Friedrich I of Württemberg, or Frederick I of Württemberg (November 6, 1754 - October 30, 1816) became Duke of Württemberg in 1797 on the death of his father: he assumed the title of Elector in 1802, and the title of King in 1806.

When he became King, he styled his children and further male-line descendants as HRH Princes and Princesses of Württemberg, and he styled his siblings as HRH Dukes and Duchesses of Württemberg.

He was obese: behind his back he was known as "The Great Belly-Gerent", and Napoleon Bonaparte later remarked that God had created the Prince to demonstrate the utmost extent to which the human skin could be stretched without bursting.

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Duke of Württemberg | width="40%" style="text-align: center;" |Elector of Württemberg
1803-1805 | width="30%" |Succeeded by:
became King of Württemberg

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Elector of Württemberg | width="40%" style="text-align: center;" |King of Württemberg
1805-1816 | width="30%" |Succeeded by:
Wilhelm I