Konrad Alexander Friedrich Duden (3 January 1829 – 1 August 1911) was a German philologist and teacher.

After receiving his Abitur in 1846 in Wesel, Duden studied history, Germanistics, and classical philology at Bonn.

It was here he published his most important work, the "Complete Orthographic Dictionary of the German Language" (Vollständiges Orthographisches Wörterbuch der deutschen Sprache).

In 1902, the German parliamentary upper house ("Bundesrat") made his rules for orthography mandatory in official state documents.

One hundred years after his death, the Duden dictionary remains the authoritative source for German orthography.