History of Morgan’s Cavalry. Cincinnati: Miami Printing and Publishing, 1867, 1st edition.
Duke (1838-1916) was a Kentucky native practicing law in St. Louis before the Civil War broke out. Involved in secessionist activities, he joined Morgan’s company of Lexington rifles when the war finally erupted, and succeeded Morgan after his death. Two weeks later, Duke was commissioned Brig. Genl. When word reached him of Lee’s surrender, he hastened to the aid of Johnston in North Carolina, and his unit formed part of Jefferson Davis’ escort to Georgia. Duke’s three years with Morgan in the thick of the war, and being Morgan’s second in command, made him one of the premier biographers of the famous guerilla commander. Once the war ended, Duke settled in Louisville and worked as hard for swift reconciliation as he had for secession.
Source: Cowan’s Auction, online