Count Carl Gustaf Mannerheim (August 10, 1797 Lemu–October 9, 1854 Stockholm) was a Swedish entomologist of German ancestry and governor of Viipuri province.
From 1819 he served as the secretary to the Finnish Minister Secretary of State in Saint Petersburg. In 1833 he was appointed governor of the Vaasa Province and soon after of the Viipuri and Savonlinna County. From 1839 until his death he served as the chief judge of the newly formed Imperial Court of Appeals (“Kayserlichen Hofgerichtes” , hovioikeus) in Viborg.
He was decorated with the Cross of the Order of Saint Stanislaus and was made a knight of the Order of Saint Vladimir. He published many papers on Coleoptera and worked on the collections of the natural history museums of Dorpat, Saint-Petersburg and Moscow.
Mannerheim was a member of the St Petersburg Academy of Sciences (1827) and of the Finnish Society of Sciences and Letters (1838) and a foreign member of the Royal Swedish Academy of Sciences (1852).
He was married to Eva Wilhelmina Schantz who was one of the leading figures in Finnish society life. His grandson Baron Carl Gustaf Emil Mannerheim (1867–1951) became Marshal and President of Finland.