John Ker (1789–1850) was an American surgeon, planter and politician in Louisiana.
Together with several major Mississippi planters, in the 1830s Ker co-founded the Mississippi Colonization Society, promoting removal of free American blacks to a colony in West Africa (later Liberia).
The state group modeled itself after the American Colonization Society, where Ker later served as a vice president.
Born in North Carolina, where his father was the first president of the new state university, Ker moved with his family as a youth to Mississippi after 1817, when his father was appointed to the state supreme court.
He went to medical school in Philadelphia, Pennsylvania and returned to the South.
Serving as a surgeon in the War of 1812 and Creek War, Ker later owned a cotton plantation in Louisiana and served in the state house.