Karl Georg August, Hereditary Prince of Brunswick-Wolfenbüttel (English: Charles George Augustus; 8 February 1766 – 20 September 1806) was the heir to the Duchy of Brunswick as the eldest son of Charles William Ferdinand, Duke of Brunswick-Wolfenbüttel and Princess Augusta of Great Britain.

Prince Karl was born mentally ill and blind, and Louise was reportedly more of a caretaker than a spouse to him, who was described as totally dependent of her.

The Swedish Princess Hedwig Elizabeth Charlotte described him, as well as his family, at the time of a visit in August 1799: Our cousin, the Duke, arrived immediately the next morning.

As a noted military man he has won many victories, he is witty, literate and a pleasant acquaintance, but ceremonial beyond description.

The Hereditary Prince, chubby and fat, almost blind, strange and odd – if not to say an imbecile – attempts to imitate his father but only makes himself artificial and unpleasant.

The other son, Prince Georg, is the most ridiculous person imaginable, and so silly that he can never be left alone but is always accompanied by a courtier.