Prince Charles of Hesse-Kassel (Danish: Carl af Hessen-Kassel; German: Karl von Hessen-Kassel; 19 December 1744 – 17 August 1836) was a cadet member of the house of Hesse-Kassel and a Danish general field marshal. Brought up with relatives at the Danish court, he spent most of his life in Denmark, serving as royal governor of the twin duchies of Schleswig-Holstein from 1769 to 1836. Charles was born in Kassel on 19 December 1744 as the second surviving son of Hesse-Kassel's then hereditary prince, the future Frederick II, Landgrave of Hesse-Kassel (or Hesse-Cassel) and his first wife Princess Mary of Great Britain. His mother was a daughter of King George II of Great Britain and Caroline of Ansbach and a sister of Queen Louise of Denmark. Charles began a military career in Denmark. In 1758 he was appointed colonel, at the age of 20 major general and in 1765 was put in charge of the artillery. After his cousin, King Christian VII, acceded to the throne in 1766, he was appointed lieutenant general, commander of the Royal Guard, knight of the Order of the Elephant and member of the Privy Council. Also in 1766, he was appointed Governor-General of Norway, a position he held until 1768 but which remained mostly titular, as he never went to Norway during this period. In 1763, his elder brother William married their first cousin, Danish Princess Caroline. Charles followed suit on 30 August 1766 at Christiansborg Palace — his wife was Louise of Denmark, and Charles thus became brother-in-law to his cousin, King Christian VII. In 1769, Prince Charles of Hesse was appointed royal Governor of the twin duchies of Schleswig and Holstein on behalf of the government of his brother-in-law, King Christian VII of Denmark and Norway. Charles took up residence at Gottorp Castle in Schleswig with his family. In September 1772, Charles was appointed commander-in-chief of the Norwegian army and he and Louise moved to Christiana. The assignement was a consequence of the coup d'état of King Gustav III of Sweden on 19 August 1772 and the subsequent prospect of war with Sweden. Even though Charles returned to Schleswig-Holstein in 1774, he continued to function as commander-in-chief of the Norwegian army until 1814. At the time of his return from Norway, he was appointed field marshal.

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