Joel Roberts Poinsett, American physician and politician, 15th United States Secretary of War (died 1851)

Joel Roberts Poinsett was an American physician, botanist, politician, and diplomat. He was the first U.S. agent in South America, a member of the South Carolina Legislature, and later a United States Representative from 1821 to 1825. In 1825, he was appointed by John Quincy Adams as the first United States Minister to Mexico, replacing James Wilkinson, and serving through the first year of Andrew Jackson's administration in 1829. He represented the United States government to the First Mexican Empire, the Provisional Government, and the First Mexican Republic in Mexico City.

The secretary of war was a member of the U.S. president's Cabinet, beginning with George Washington's administration. A similar position, called either "Secretary at War" or "Secretary of War", had been appointed to serve the Congress of the Confederation under the Articles of Confederation between 1781 and 1789. Benjamin Lincoln and later Henry Knox held the position. When Washington was inaugurated as the first President under the Constitution, he appointed Knox to continue serving as Secretary of War.