George McClellan and Nelly his wife
Lincoln was a pragmatist who wore simple black suits of a country lawyer. George McClellan was a Dandy. He was overly confident, and full of himself. While Robert E. Lee dressed as a Colonel, so as not to be overbearing in his authority. McClellan was anal about preparations and as such he took his time. He would not be rushed and he would not be lectured.
Lincoln on the other hand was growing utterly frustrated at McClellan’s tentative nature. On November 5th, 1862, Lincoln removed McClellan.
Edwin M. Stanton, Secretary of War, United States to Lincoln about McClellan: If he had a million men he would swear the enemy has two million, and then he would sit down in the mud and yell for three.
General McClellan had raised a powerful army, but seemed disinclined to actually seek battle. So Lincoln sent him a letter: “My dear McClellan: If you don’t want to use the Army I should like to borrow it for a while.”
On the complaint that he move his forces faster, McClellan announced that his horses needed rest. “Will you pardon me for asking what your horses have done since Antietam?” Asked Lincoln.
Incensed that Lincoln was offering where to move forces, McClellan simply defied him. Lincoln sent him a message that read in part: “the commanding general cannot lightly regard such marked departure from the tenor of his instructions.””
Sources: Wikipedia; NYT Paul Krugman; A Fierce Glory: Antietam–The Desperate Battle That Saved Lincoln and Doomed Slavery” by Justin Martin.