A.J. Smith in 1864-65. His command of the 16th Corps Right Wing was one of the few bright spots of the Red River Campaign.
After Sturgis' defeat at Brices' Crossroads, the 16th Corps Right Wing was tasked with entering Forrest's country and keeping him occupied, and with the hope of defeating him in battle. Smith handled the campaign very well, with the obvious exception of neglecting to have his rations properly inspected. Nonetheless, Smith's tactical and strategic handling of his small army, both in battle, and on the march, was exceptional, and he administered a good whipping to the rebels.
Smith and his corps (now titled Detachment - Army of the Tennessee), were next sent to Missouri in response to Prices' Raid. I don't know much about his activities here, if anyone would like to chime in.
Smith's next assignment was under Thomas at the Battle of Nashville. As we all know, on both days, his corps smashed through the Confederate lines and drove them in utter route.
Finally, he successfully forced the surrender of Spanish Fort in April 1865.
I don't believe it was actually intended as such, but Smith's Guerrilas served as a defacto strategic reserve for the Western Theater.