Robert M. Utley, "Custer, George Armstrong," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00290.html.
Custer found his calling in the Civil War. Two years of staff duty, including a tour as aide to General George B. McClellan (1826-1885), established his military skill, both as a staff officer and in combat. So impressed was General Alfred Pleasonton, commander of the Cavalry Corps of the Army of the Potomac, that he recommended Custer for promotion. In June 1863 Captain Custer was appointed brigadier general of volunteers and given command of the Michigan Cavalry Brigade. At twenty-three, he was the youngest general in the Union army. Almost instantly General Custer made a dazzling name for himself. On the third day of Gettysburg the Michigan Brigade played a key role in turning back General J. E. B. Stuart's Confederate cavalry, which threatened the Union rear at the very moment of George Edward Pickett's charge on the Union center. Thereafter Custer's successes accumulated one after another. He became known throughout the army for smashing cavalry charges, for heedless bravery, for tactical brilliance more instinctive than cerebral, for heavy casualties, and, with long yellow hair and gold-bedecked black uniform, for personal flamboyance. Newspapers made him a household name.