Perhaps a more appropriate answer would be the Commanders in Chief of the North and South, other than the President himself. There were, of course, many subordinate generals who were also important, but whose place in history is more trivia than consequence. The South had only one commander in chief; Robert E. Lee. Lee had previously been offered command of Union forces by General Winfield Scott, but had turned down the offer as he could not bring himself to fight against his native Virginia. He later resigned his commission in the U.S. Army and joined the Confederate cause.

Lee managed to defeat most of the Union commanders in chief who were routinely removed from command after their defeat; this in accordance with standard army policy. The first commander was General George McClellan who was fired after Bull Run. Later, General U.S. Grant was defeated at Shiloh by Gen. Albert Sidney Johnson on the Confederate side. Grant was removed and replaced by Henry "Old Brains" Halleck. Halleck was defeated by Lee and replaced with McClellan once again. McClellan was too timid to attack Confederate forces following a Union victory at Antietam, and was fired a second time, this time permanently, and replaced by Gen. Ambrose G. Burnside. Burnside wore his whiskers far down his cheeks; thus the term "sideburns." Burnside was defeated by Lee at Fredericksburg and ultimately replaced with "Fighting Joe Hooker." Hooker was defeated by Lee at the Battle of Chancellorsville, and replaced with U.S. Grant once again following Grant's victory at Vicksburg and  who prosecuted the war to its conclusion.