It's Muhammad Ali. Unquestionably.

Greatest self-promoter in boxing history, always heading up his own parade.

Lots of guys bring attention to themselves as well they should; it brings up the gate and sells more tickets. Nobody did it to Ali's extent though. Other huge draws like Dempsey and Tyson would do interviews and appearances and whatnot as it's part of a Champion's job, but they didn't go out of their way to create publicity; the fans and press just went to them. Ali, on the other hand, always went that extra mile for more and more publicity which is a good career move. Good publicity, bad publicity, didn't matter, just as long as it sold tickets.