Civil War Union Brigadier General. He studied law, was admitted to the Ohio Bar Association, and practiced as an attorney in Cincinnati, Ohio. He was elected as a Democrat to the Ohio General Assembly where he struck a fellow assemblyman and was expelled, prompting him to move to Denver, Colorado, in 1860. When the Civil War began, he entered the service as the Captain of the 1st Colorado "Pike's Peakers" Volunteer Regiment, and soon became a Colonel. Colorado was a federal territory that bordered the Confederate territory of New Mexico. When Confederate invaders under the command of General William R. Scurry threatened Colorado, Slough was ordered to remain at Fort Union, New Mexico Territory. He disobeyed his orders and led a detachment from his regiment to pursue the Confederates, hoping to intercept them at Glorieta Pass. He won total victory when he sent Major John M. Chivington on a flank attack, which successfully destroyed a Confederate supply train. Slough barely escaped with his life when "his own men became so disgusted with him for keeping so far to the rear of the action that they turned a howitzer on him and opened fire." The Battle of Glorieta was a turning point in the confederate invasion of New Mexico, and ironically, Colonel Slough received some of the credit. Slough was ordered by his superior, Colonel Edward Canby, to return to the fort at once. Fearing reprimand, he sent announcement of his resignation ahead of him, departed Colorado, and returned to the East. He reported to Washington, and was assigned to command a brigade in the Shenandoah Valley. From Abraham Lincoln, he received a brevet promotion from Colonel to Brigadier General of U.S. Volunteers on August 25, 1862, and was reassigned to Alexandria, Virginia, as a military Governor. He remained there for the rest of the war. Later, Slough was one of the pall bearers at Lincoln's funeral. He was appointed by President Andrew Johnson, in March of 1866, as chief justice of the New Mexico Supreme Court. Slough was a hard working judge, and because of his military background was able to work well with military commanders. However, he became unpopular as a judge with the Santa Fe Ring, and many officials sought his removal. He was shot from a pistol wielded by legislator William L. Rynerson during a quarrel on December 15, 1867, which left him mortally wounded. He died two days later.