Theodor Joseph Hagen (24 May 1842, Düsseldorf – 12 February 1919, Weimar) was a German painter and art teacher.

[1] In 1871, he was summoned to the Weimar Saxon-Grand Ducal Art School to teach landscape painting as a replacement for Max Schmidt, who had left to take another position.

He was head of the art department from 1876 to 1881, but grew tired of his administrative duties and returned to teaching.

[1] Through his friendship with Alfred Lichtwark, the first Director of the Kunsthalle Hamburg, he spent some time there, painting scenes of the harbor and the North Sea.

A street in Weimar has been named the Theodor-Hagen-Weg in his honor and his home (now Trierer Straße 36) is a municipal monument.