Mather Byles Brown was an American artist, born in Boston, who came to London at an early age and probably became a pupil of Benjamin West. Although he was described in 1789 as Portrait-Painter to the Duke of York, this and 405135 are the only two paintings by him in Royal Collection. Mather Brown had a long career, exhibiting at the Royal Academy for nearly fifty years between 1782 and his death in 1831.

This portrait represents the military commander William von Freytag, Field-Marshal in command of the Hanoverian contingent in a campaign against the French in the Low Countries. He is depicted in a blue Hanoverian uniform with red facings, and gold buttons and epaulettes, and a short powdered wig. 

The sitter was closely associated with the royal family, but was disliked by the eldest Princes. Mather Brown also painted a picture, later engraved by S.W. Reynolds, depicting the rescue of Field-Marshal von Freytag and Prince Adolphus after they had blundered into a French picquet at Rexpoede on 6th September 1793.