François Jean de Beauvoir, Marquis de Chastellux, was a military officer who served during the War of American Independence as a major general in the French expeditionary forces led by general Comte de Rochambeau. Being on general Rochambeau's staff for the duration of the war, Chastellux acted as the principal liaison officer between the French commander in chief and George Washington. After arriving in America in July 1780, Chastellux participated to the American Revolutionary War as Major General in the French expeditionary force led by general Rochambeau. During the following year, he was third in command of the French forces engaged at the decisive Siege of Yorktown in 1781 where the British were ultimately defeated. After his return to France, Chastellux also remained in contact with Thomas Jefferson, now the American representative in Paris, whom he had previously visited on his Virginia estate at Monticello. He was elected both a Foreign Honorary Member of the American Academy of Arts and Sciences, and of the American Philosophical Society.