After the Thrilla in Manilla, he should have set up the 3rd fight with Norton, fought him in early to mid '76 and retired. There was nothing left to prove after complete the trilogy with Frazier and Norton. Jimmy Young, Earnie Shavers, Evangelista... he had nothing to prove against these guys.

Ali retires after completing the trilogy with Norton in early to mid '76 and retires at 34.