Theodor Friedrich Julius Basiner was a Baltic German botanist who lived and worked mainly in Imperial Russia.

Theodor Gartner was an Austrian linguist, Romance philologist and professor.

Theodor Gomperz, Austrian philosopher and classical scholar, was born at Brno (Brünn).

Theodor Gottlieb von Hippel was a German satirical and humorous writer.

Theodor Hagen [often spelled Theodore Hagen] was a writer on musical topics in Germany and the United States. He was a member of the local Communist League in Hamburg, Germany and took part in the publication and distribution of the Neue Rheinische Zeitung Politisch-ökonomische Revue.

Theodor Hell was the pseudonym of Karl Gottfried Theodor Winkler, a court councillor (Hofrath) in Dresden from 1824, who was the centre of literary life through his work as editor, translator and critic. He was the theatrical secretary from 1815.

Theodor Hertzka, or Hertzka Tivadar was a Jewish-Hungarian-Austrian economist and journalist.

Theodor Hirsch was a German historian who was a native of Altschottland, Danzig. He was a cousin to historian Siegfried Hirsch (1816-1860).

Theodor Willem Johannes Juynboll also: Theodorus Willem Johannes Juijnboll, Theodorus Guiliemus Johannes Juynboll was a Dutch Reformed theologian and oriental philologist.

Theodor Kallifatides is a writer. He is a Greek immigrant to Sweden, and writes in Swedish.