Wilhelm Böttner trained in Kassel with Johann Heinrich Tischbein the Elder, travelling during the 1770s to Paris and Rome, where he was inspired by the work of Raphael. He was invited back in 1781 by Frederick II of Hesse-Kassel, and after a further brief stay in Paris, he worked for the rest of his life in the service of the court in Kassel, enjoying great success as a portrait and history painter.

William IX was George III's first cousin - his mother was Princess Mary (1723-72), the sister of George III's father, Frederick, Prince of Wales. He inherited the title Landgrave of Hesse-Cassel upon the death of this father in 1785 and was subsequently in 1803 granted the title of Elector of Hesse. One of the richest princes in Europe, his employment of Mayer Amschel Rothschild (1744-1812) as 'Court Factor' effectively launched the fortunes of that family. Wilhelm also built in 1785 a new range of palace buildings and an English landscape garden to the Wilhelmsöhe Park in the hills above Kassel.

The sitter appears here three-quarter-length, in military uniform with the sash and badge of the Order of the Black Eagle. He sits at a desk on which are a pen and an extinguished candle and holds a letter on which is inscribed 'To Sir William Fawcitt London'.