James Longstreet (January 8, 1821 – January 2, 1904) was one of the foremost Confederate generals of the American Civil War and the principal subordinate to General Robert E. Lee, who called him his "Old War Horse." He served under Lee as a corps commander for many of the famous battles fought by the Army of Northern Virginia in the Eastern Theater, but also with Gen. Braxton Bragg in the Army of Tennessee in the Western Theater. Biographer and historian Jeffry D. Wert wrote that "Longstreet ... was the finest corps commander in the Army of Northern Virginia; in fact, he was arguably the best corps commander in the conflict on either side."
He enjoyed a successful post-war career working for the U.S. Government as a diplomat, civil servant, and administrator. However, his conversion to the Republican Party and his cooperation with his old friend, President Ulysses S. Grant, as well as critical comments he wrote in his memoirs about General Lee's wartime performance, made him anathema to many of his former Confederate colleagues. Authors of the Lost Cause movement focused on Longstreet's actions at Gettysburg as a primary reason for the Confederacy's loss of the war. His reputation in the South was damaged for over a century and has only recently begun a slow reassessment.James Longstreet in Wikipedia