With his great friend (from childhood on), the hilarious, one-of-a-kind Wally Cox (1924-1973).
As noted on both their Wikipedia pages: Brando's close friendship with Cox was the subject of rumors. Brando told a journalist: "If Wally had been a woman, I would have married him and we would have lived happily ever after." Two of Cox's wives, however, dismissed the suggestion that the love was more than platonic.