Charles (Karl) was ruling as Prince of Wolfenbüttel from 1735 until his death.
Charles was the eldest son of Ferdinand Albert II, Duke of Brunswick-Lüneburg and Antoinette Amalie of Brunswick-Wolfenbüttel.
He founded the Collegium Carolinum, an institute of higher education which is today known as the Technical University of Brunswick. He also hired Gotthold Ephraim Lessing as the librarian for the Bibliotheca Augusta, the ducal library.
Charles attempted to promote the economic development of his state; he did not manage to keep the state finances in check. As a consequence, in 1773 his eldest son Charles William Ferdinand took over government.
In 1733, Charles married Philippine Charlotte, daughter of King Frederick William I of Prussia. They had the following children that reached adulthood:
Charles William Ferdinand (1735–1806)
Sophie Caroline Mary (1737–1817), married Frederick, Margrave of Brandenburg-Bayreuth
Anna Amalia (1739–1807), married Ernest Augustus II, Duke of Saxe-Weimar-Eisenach
Frederick Augustus (1740–1805)
Albert Henry (1742–1761), died childless
William Adolf (1745–1770), died childless
Elizabeth Christine Ulrike (1746–1840), married King Frederick William II of Prussia (divorced)
Augusta Dorothea, Abbess of Gandersheim (1749–1803)
Maximilian Jules Leopold (1752–1785), died childless
Charles also had a child out of wedlock, Christian Theodor von Pincier (1750–1824), the adopted son of Baron von Pincier of Sweden.
Philippine Charlotte von Preussen
Leopold von Braunschweig-Wolfenbüttel