Nice work by Longform hipping us to this 1979 article by Roger Ebert about watching Rocky II with Muhammad Ali:

He watched the opening scenes of Rocky II in silence, not speaking until the scene in which Apollo Creed, the heavyweight champ, delivers a televised challenge designed to taunt Rocky back into the ring.

"That's me, all right," Ali said "Apollo sounds like me. Insulting the opponent in the press, to get him psyched out. That's me exactly."

Back home at Rocky's new house, the doorbell rang.

"You know who that's gotta be," Ali said. "That's gotta be his trainer." And, yes, Rocky opened the door and his old trainer, Mickey, was standing there on the doorstep.

"That's how Angelo Dundee used to get me," Ali remembered. "A good trainer knows a good fighter can't stand to have people talk about him bad on television."

Mickey was giving Rocky advice: "We got to get you fighting with your other hand. Use your right, save your left, protect that bad eye..."

"It just maybe could be," Ali said, "that if you started on a kid at seventeen or eighteen, by the time he was twenty-two you could change the hand he leads with. But not overnight it can't be done."