Lieutenant John Ross - Public domain portrait painting

Caption from the museum's website

Lt. John Ross of the 34th Regiment was a distinguished member of the British Army. After the final campaigns of the French and Indian War, he explored and mapped the Mississippi Valley before rotating back to Great Britain with his regiment in the later 1760s. Ross returned to America in 1776 and participated in a number of battles in the North. This portrait, attributed to Scottish-born artist David Martin c. 1769, depicts Ross after his first American tour of duty.