Fighters whose personality/characteristics are different than their fighting style

[Sleepwalker]

Floyd. Obvious choice here. Listen to him talk, you'd believe he has been knocking people thru the ropes in every fight.

Winky Wright. One of the best defensive fighters in the modern era who was quite conservative at times, he is quite a high-risk player at the crap table. He really is. This dude presses his bets to no avail.

[Vendettos]

Foreman was the best of both extremes

Young George Foreman - Powerhouse bomber, fairly grumpy and looks angry always outside the ring.
Older George Foreman - Powerhouse bomber, but the nicest guy who found Jesus outside the ring.

[Master]

Tyson, shy and quiet who had little confidence but in the ring total beast.

[Dark Lord Al]

David Haye , outside the ring he is flash brash and cocky.
I have yet to remember what he is like in the ring as he always cancels his fights.

[superheavyrhun]

Mike Tyson is typical, most boxers I've encountered have a persona they use to sell fights, but most of them are humble and down-to-earth outside the ring. In terms of Brits, those I've spoken to include Jamie Moore and Clinton Woods who were both friendly and self-deprecating, but were very competitive in the ring.

The one exception I came across was Anthony Small, who was arrogant, cocky and brash, while in the ring he was ultra cautious and didn't want to get anywhere near a punch coming his way. And then he went all jihad.

[Primo Carnera]

Bellew and Johnny Nelson - both are brash and cocky and talk like they're KO merchants, but both are boring to watch.
Whereas Nigel Benn in his early days with his little innocent voice and lisp, yet went out for a "right old tear up!"

[Spicoli]

Terry Norris was one of the most soft spoken unassuming guys in interviews etc but in the ring he had a chip on his shoulder and went all out to fight, inside and outside some rules