A Union Army veteran with southern sympathies. Probably someone from my neck of the woods in rural southwestern PA. Obviously an anti-war unionist who eventually served in the army and came to respect Grant.
Many people forget that although Pennsylvania was a big Union state, it still had plenty of Copperheads. Most people think of NYC Irish Catholics as being the primary agitators, but there were a strong number rural Pennsylvanians that were less than thrilled with the war, even near Gettysburg itself.
In Greene County, which is not too far from here, they have an old cemetery called "N*gger Cemetery". In fact, there was talk that Greene County, which is the southernmost county here in the west, would join the Confederacy.
However, as you say, Rural Pennsylvanians (and Ohioans for that matter) were not especially predisposed to disliking the south. I can see a voter around here, a Democrat, thinking Breckinridge was the right candidate to keep the union from breaking apart and for keeping slaves in their place. Now, that fella gets drafted, right? Well, he still supports the union cause because he's a patriot, but his political views haven't much changed. He also would see McClellan as a hero and would've loved him, as most of McClellan's soldiers did... But then this fella later serves under Grant and Grant makes an impression on him because Grant, to start, favored a lenient policy to the south, as Johnson did, so that admiration turns into loyalty.
It is somewhat of a stretch though that this particular person would not have supported Horatio Seymour in 1868, while in 1872 seeing Horace Greeley as a crank. Seymour was one of the most respected Democratic leaders in the country, but I can only think that this individual would've transferred their loyalty to Grant based on service in the army.