John A. Logan (1826–1886) was a native of Illinois who served as a second lieutenant in the Mexican–American War before studying at the University of Louisville to become a lawyer. Originally a member of the Democratic Party, he was elected state senator and later a member of the U.S. House of Representatives. During the onset of the Civil War, Logan denounced what he considered extremists on both sides, but eventually volunteered to fight with the Union Army during the First Battle of Bull Run. He then resigned from Congress and was made colonel after he organized the 31st Illinois Volunteer Infantry Regiment. Logan was wounded twice while serving in the war and considered an outstanding field commander. He was promoted to brigadier general following the victory at Fort Donelson. Logan played a significant role in the Union success at Vicksburg and served as that district's military governor. Following the death of General James B. McPherson, Logan was given command of the Army of the Tennessee, but was soon relieved by General Oliver O. Howard after Logan became too involved with the 1864 presidential election. He left the army in 1865 and resumed his career in politics.