Karl August Varnhagen von Ense (21 February 1785 in Düsseldorf – 10 October 1858 in Berlin) was a German biographer, diplomat and soldier.
He was born in Düsseldorf, the younger brother of Rosa Maria Varnhagen, a noted poet, writer, and educator. He studied medicine in Berlin, but most of his time was spent examining philosophy and literature, which he later studied more thoroughly at Halle and Tübingen. He began his literary career in 1804 working along with Adelbert von Chamisso on his Berliner Musenalmanach.
In 1809, he joined the main Austrian army under Archduke Charles, serving in IR20 Reuss-Plauen at the Battle of Wagram, where he was wounded. He was then made adjutant to Prince Bentheim, whom he accompanied to Paris, where he continued his studies. In 1812, he entered the Prussian civil service in Berlin but soon left to enter the Russian service as captain. He served in Tettenborn's corps as adjutant to Tettenborn on trips to Hamburg and Paris. He recorded his experiences in Geschichte der Hamburger Ereignisse (History of the events in Hamburg; London, 1813) and Geschichte der Kriegszüge Tettenborns (History of Tettenborn's Campaigns, 1814). He worked as a tutor and butler in the homes of several families of the wealthy Jewish bourgeoisie. This allowed him to learn from an early age young characters in his time, some already famous, such as: Adelbert von Chamisso, Justinus Kerner, Friedrich de la Motte Fouqué, Ludwig Uhland and many other poets of romanticism.