In August 1862, nineteen-year-old Edward G. Granger joined the 5th Michigan Cavalry Regiment as a second lieutenant. On August 20, 1863, the newly promoted Brig. Gen. George Armstrong Custer appointed Granger as one of his aides, a position Granger would hold until his death in August 1864. Many of the forty-four letters the young lieutenant wrote home during those two years, introduced and annotated here by leading Custer scholar Sandy Barnard, provide a unique look into the words and actions of his legendary commander. At the same time, Granger's correspondence offers an intimate picture of life on the picket lines of the Army of the Potomac and a staff officer's experiences in the field. As Custer's aide-de-camp, Lieutenant Granger was in an ideal position to record the inner workings of the Michigan Brigade's command echelon. Riding at Custer's side, he could closely observe one of America's most celebrated and controversial military figures during the very days that cemented his fame. With a keen eye and occasional humor, Granger describes the brigade's operations, including numerous battles and skirmishes. His letters also show the evolution of the Army of the Potomac's Cavalry Corps from the laughingstock of the Eastern Theater to an increasingly potent, well-led force. By the time of Granger's death at the Battle of Crooked Run, he and his comrades were on the verge of wresting mounted supremacy from their Confederate opponents. Amply illustrated with maps and photographs, An Aide to Custer gives readers an unprecedented view of the Civil War and one of its most important commanders, and unusual insight into the experience of a staff officer who served alongside him.