Newly graduated from West Point, Custer joined the Army of the Potomac in 1861 and commanded a cavalry brigade with distinction at First Bull Run (Manassas). His reputation as a fearless leader grew as he fought throughout the Peninsular Campaign of 1861-1862. At the age of twenty-three, he became the youngest general in the Union Army.
Many of those who served under Custer (called "the boy general") admired him; others accused him of recklessness and glory hunting. He would remain a controversial figure throughout his career, but his Civil War record was outstanding. In 1863 he pursued Confederate forces retreating from Gettysburg and engaged then at Battle Mountain, Virginia. His greatest triumph came in 1865, when he hounded Lee's retreating army until the surrender at Appomattox. It was Custer who accepted the Confederate flag of truce. After the war, he joined the Seventh Cavalry Regiment and fought in the Sioux Wars until the fated ambush of 1876 at the Little Big Horn River, where he was killed.