Karl, Duke of Schleswig-Holstein-Sonderburg-Glücksburg

Karl, Duke of Schleswig-Holstein-Sonderburg-Glücksburg (30 September 1813 – 24 October 1878) was Duke of Schleswig-Holstein-Sonderburg-Glücksburg from 1831 to 1878. Karl was the eldest son of Friedrich Wilhelm, Duke of Schleswig-Holstein-Sonderburg-Glücksburg, and Princess Louise Caroline of Hesse-Kassel and an elder brother of Christian IX of Denmark.

Upon his father's death in 1831, Karl inherited Glücksburg Castle and became Duke of Schleswig-Holstein-Sonderburg-Glücksburg at the age of seventeen. In 1838, he became the son-in-law of King Frederick VI of Denmark when he married the his cousin, Princess Vilhelmine Marie of Denmark. A supporter of the Schleswig–Holstein movement, Duke Karl actively sided against Denmark during the First Schleswig War from 1848 to 1851, which caused the duke's relations with the Danish Royal family to be severed. The ducal couple lived abroad until an uneasy reconciliation was established in 1852. In 1854, he had to cede the family seat Glücksburg Castle to King Frederick VII of Denmark. During the Second Schleswig War in 1864, the ducal couple left the country again, only to return again the following year after the Prussian victory. In 1871, after long negotiations with the Prussian Government, the Duke again took possession of Glücksburg Castle. Upon the death of the childless duke, the ducal title was inherited by his younger brother, Friedrich.