Karl Wilhelm Theodor Frenzel (6 December 1827 – 10 June 1914) was a German novelist, essayist and theatre critic.
In 1861 he joined the editorial staff of the liberal Berlin National-Zeitung, of which he was head of the feuilleton and theatre critic until 1908.
His influential position was unchallenged for a long time and only weakened when Gerhart Hauptmann and others were joined by Naturalism, whom Frenzel, in contrast to Fontane, condemned and fought against.
Frenzel died on 10 June 1914 at 86 in his Berlin apartment at Dessauer Straße 19 and was buried in the Invalids' Cemetery on Scharnhorststraße.
Frenzel initially turned to the genre of the historical novel and wrote a number of narrative works, the plot of which was preferably set in the 18th century, during the period of the Enlightenment with its then predominant French education.