William R. Terrill was a Virginia-born Union general during the American Civil War (1861–1865). Three of his brothers fought for the Confederacy, two of whom died, including James B. Terrill, who was killed in 1864. Disowned by his family, William Terrill distinguished himself in the Western Theater of the war, including at the Battle of Shiloh in April 1862. A strict disciplinarian, he was "a drunken old tyrant" in the words of one soldier. Others were more sympathetic, with a Union captain arguing that he was "a first rate fighting man." Terrill was promoted to brigadier general in September 1862 and, in October, commanded a brigade at the Battle of Perryville, Kentucky, where he struggled with coordinating both infantry and artillery, raw recruits and professional soldiers. He was killed in the fighting.

William Rufus Terrill was born in Covington, Virginia, in the Allegheny Highlands, on April 21, 1834, the son of William H. and Elizabeth Pitzer Terrill. He attended the United States Military Academy at West Point, New York, and was a good student. One incident marred his record, however. Terrill fought fellow cadet Philip H. Sheridan after Sheridan attacked him with a bayonet. Sheridan, who would also go on to be a Union lieutenant general, was suspended for a year, but Terrill graduated in 1853, finishing sixteenth out of fifty-two cadets. He entered the U.S. Artillery, fought in Florida during the Second Seminole War (1835–1842), taught mathematics at West Point, and served in Kansas during the 1850s, when proslavery and antislavery settlers—among them John Brown—battled each other.

Terrill was one of 44 (out of a total of 126) Virginia-born West Point graduates who, in 1861, remained loyal to the United States Army. The most famous of these was George H. Thomas, and like Thomas, Terrill credited the army for educating and molding him. Also like Thomas, Terrill was married to a Northerner, Emily Henry. In both instances, some historians have speculated that this may have influenced the decision to remain in the U.S. Army. In May 1861, Terrill became captain of the 5th U.S. Artillery. His angry father disowned him, threatening to strike his name from the family records.

While Terrill's siblings fought in the Eastern Theater, he went west. On April 6–7, 1862, he commanded artillery at the Battle of Shiloh, Tennessee, earning enough acclaim to win promotion to brigadier general in September. That autumn, Terrill commanded an infantry brigade when Confederate forces invaded Kentucky. When Union troops were attacked at Perryville on October 8, 1862, Terrill's infantry held the Union's extreme left flank. Accustomed to commanding artillery, Terrill mishandled his infantry, most of whom were raw recruits. His soldiers were battered back, and some of Terrill's men later complained that the general's obsession with the cannon led to the collapse of his brigade, which suffered 22 percent casualties.

Terrill fell back, reorganized his command, and returned to the fight to support another brigade on the Union left flank. While he walked up the back slope of a hill, a Confederate artillery shell exploded overhead and shrapnel ripped through his chest. He asked a nearby officer, "Major, do you think it's fatal?" Terrill then muttered, "My poor wife, my poor wife." Taken to a nearby farmhouse, he died less than ten hours later. Terrill was buried at West Point.

Two of Terrill's brothers, James and Philip, were killed fighting for the Confederacy. According to legend, their father placed a monument to his slain sons that read, "This monument erected by their father. God alone knows which was right."