Reuben D. Mussey Jr. (often called RD Mussey) (May 30, 1833 – May 29, 1892) was a Union Army colonel during the American Civil War and a distinguished lawyer. He was an important recruiter of black men into the United States Colored Troops. Between April 1865 and November 1865, Mussey was President Andrew Johnson's private secretary. Johnson nominated Mussey for appointment to the brevet grade of brigadier general of volunteers, but the U.S. Senate did not confirm the appointment. Mussey was the husband of Ellen Spencer Mussey who was also his law partner and became the head of the practice upon his death.