Rudolph Augustus, a member of the House of Welf, was Duke of Brunswick-Lüneburg and ruled as Prince of Brunswick-Wolfenbüttel from 1666 until his death. In 1685 he made his younger brother Anthony Ulrich co-ruler.

The Duchy of Brunswick-Lüneburg, or more properly the Duchy of Brunswick and Lüneburg, was a historical duchy that existed from the late Middle Ages to the Late Modern era within the Holy Roman Empire, until the year of its dissolution. The duchy was located in what is now northwestern Germany. Its name came from the two largest cities in the territory: Brunswick and Lüneburg.