Albert Sidney Johnston

Albert Sidney Johnston (February 2, 1803 – April 6, 1862) served as a general in three different armies: the Texian Army, the United States Army, and the Confederate States Army. He saw extensive combat during his 34-year military career, fighting actions in the Black Hawk War, the Texas War of Independence, the Mexican–American War, the Utah War, and the American Civil War.
Considered by Confederate States President Jefferson Davis to be the finest general officer in the Confederacy before the later emergence of Robert E. Lee, he was killed early in the Civil War at the Battle of Shiloh on April 6, 1862. Johnston was the highest-ranking officer, Union or Confederate, killed during the entire war. Davis believed the loss of General Johnston "was the turning point of our fate."
https://en.wikipedia.org/wiki/Albert_Sidney_Johnston