James Knox Polk (1795-1849) was the eleventh President of the United States. He was responsible for the second-largest expansion of the nation's territory. Polk secured the Oregon Territory (including Washington, Oregon and Idaho), then purchased most of what became the Southwest United States through the Treaty of Guadalupe Hidalgo that ended the Mexican War.
Prior to his Presidency, Polk had served as Governor of Tennessee and, before that, as Speaker of the House of Representatives. He is the only alumnus of either office ever to be elected President, though Andrew Johnson, an unelected President who succeeded the late Abraham Lincoln to the office, had served as appointed military governor of Tennessee during the American Civil War.