King of Württemberg, from 25 June 1864 until his death on 6 October 1891. He was the son of Wilhelm I, King of Württemberg (1781–1864) and his third wife (and first cousin) Pauline Therese of Württemberg (1800–1873).
On 13 July 1846 he married Grand Duchess Olga Nikolaievna of Russia, daughter of Tsar Nicholas I and Charlotte of Prussia. Charlotte was a daughter of Frederick William III of Prussia and Louise of Mecklenburg-Strelitz. She took the name Alexandra upon her marriage. Karl acceded to the throne upon his father’s death in 1864.
The couple had no children, perhaps because of Karl’s homosexuality. Karl became the object of scandal several times for his closeness with various men. The most notorious of these was the American Charles Woodcock, a former chamberlain whom Karl elevated to Baron Savage in 1888. Karl and Charles became inseparable, going so far as to appear together in public dressed identically. The resulting outcry forced Karl to renounce his favorite. Woodcock returned to America, and Karl found private consolation some years later with the technical director of the royal theater, Wilhelm George.
In 1870, Olga and Karl adopted Olga’s niece Vera Konstantinova, the daughter of her brother Grand Duke Konstantin.
He sided with Austria in the Austro-Prussian War of 1866, but after the battle of Sadowa concluded a secret military treaty with Prussia, and took part on her side in the Franco-Prussian War of 1870–71, joining the new German Empire at the close of 1870.
He died in Stuttgart on 6 October 1891, and was succeeded as King of Württemberg by his sister’s son, Wilhelm II.
Link to Wikipedia biography