i sort of think that the round line below the 'kepi' is the brim of the hat like in my first post.
notice how he isnt holding on to the main part, he is holding above that
im sticking with TR personally
I have found out that this piece was most likely made by famous sculptor, John Quincy Adams Ward.
Subject looks too full-bodied to be McClellan, and has the likes of R.E. Lee as "trikikiwi" stated.
Attached is a sculpture of McClellan he did for comparison.
Sure looks like Major General George B. McClellan, General-in-Chief of the U.S. Army from 1861 to 1862. If so it is most likely his favorite horse, "Daniel Webster," also known as "that devil Dan."