Gustav Theodor Wegener was a Danish painter.

Theodor Wegener was the son of the theologian Jens Ernst Wegener (1781–1846) and his wife Birgitte, née Bindesbøll (1793–1856). He was a student of the Danish court painter Jon Gulsen Berg (1783–1864) and then studied at the Royal Danish Academy of Art in Copenhagen. As early as 1838 he sent his picture “Street Scene” to the exhibition in Charlottenborg Palace. In 1839 he went to Germany to train as a decorative painter, and worked there for a few years. After his return to Denmark, Wegener specialized in biblical and historical scenes, but also painted genre pieces and landscapes.

In 1844 he won a gold medal with his painting “ Tobias goes on a journey with the angel”. In 1855/56 he went on a study trip to Italy. From 1871 until his death in 1877 he was a teacher at the drawing school of the Copenhagen Academy. Wegener was unmarried.