In June 1861, practically unschooled, without military training or experience, Nathan Bedford Forrest (1821-1877) enlisted in the Confederate Army as a private. Yet by the Civil War's end he was a lieutenant general whose dazzling exploits and bloody victories caused him to be regarded by his Northern opponents as a "devil," by Southerners as a living legend, and by historians as the greatest cavalry commander and one of the few authentic military...