The individual charged with bringing in Josey Wales and who said, "isn't that right Mr. Wilson?" was his war time compatriot "Captain Fletcher". There was no first name given. "Captain Terrill" was the commander of the "Red Legs" and who Wales chased down and killed with his own sabre. The Red Legs were the guerrillas who killed Wales family and burned his home. They were a very real organization along the Kansas/Missouri border before and during the Civil War. And, of course Hollyweird took its license representing them.

https://warfarehistorynetwork.com/articl...-guerrilla-war/

https://www.legendsofamerica.com/red-legs-kansas/