William I of Württemberg (27 September 1781-25 June 1864) was King of Würtemberg.

He was born in Lübben, the son of Friedrich I of Württemberg (1754-1816) and his wife Augusta of Brunswick-Wolfenbüttel (1764-1788).

On 8 June 1808, at Munich, he married Karoline Charlotte Auguste of Bavaria (1792-1873), daughter of Maximilian I Joseph of Bavaria (1756-1825). They divorced in 1814.

In 1816, at St. Petersburg, he married Catherina, daughter of Tsar Paul I of Russia and Sophie Marie Dorothea of Württemberg. Later that year, he succeeded his father as King of Württemberg.

In 1820, at Stuttgart, he married Pauline of Württemberg, daughter of Ludwig of Württemberg (1756-1817) and his wife Henriette of Nassau-Weilburg (1780-1857).

By his third wife, Pauline, he had two children:

1. Catherine (1821-1898), whom by her husband Frederick of Würettemberg was mother to William II of Württemberg, and
2. Karl I (1823-1891).

William I died at Schloß Rosenstein, near Stuttgart, Germany.

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