John A. Garraty replies: The origins of nicknames are often very difficult to pin down with certainty. Several different “explanations” often coexist, chiefly because most nicknames emerge gradually. Just who thought of the name or under what circumstance may not be known even by the person named or for that matter by the namer. What makes most nicknames beyond the Billy-Jimmy-Peggy type interesting to historians is that they tend to reflect traits of character and personality that are hard to document with conventional sources. Slow Trot and Black Jack are good examples.