Copper

Copper is the deuteragonist in The Fox and the Hound and it's midquel. He is Tod's best friend, Amos Slade's youngest pet dog and Chief's adoptive son. Despite being a protagonist, he was also an antagonist in the first film when he helps Amos Slade try to kill his own friend, Tod, but in the end, he reforms as he protects Tod from his master Amos Slade, then Tod and Copper became friends again.