At the Roosters he has helped turn a culture around.
Even if he leaves the code for rugby after Sunday's grand final, his legacy will be that of not only being an outstanding player but one who has helped make the team a band of professionals.
Williams' freakish talent has never been contested, but it's his leadership and overall influence on teammates that's just as important.
Roosters great Luke Ricketson says Williams has set the benchmark for young Polynesian players, while others argue he's been the major inspiration for scrutinised halfback Mitchell Pearce to knuckle down and put his career on the right track.
Rugby league legend Ron Coote admits he was one of the hordes of Sonny Bill sceptics who had grave concerns when it was announced the rugby union convert had signed a one-year deal to return to the NRL.
But Coote is one of the converted.
With the exception of the most hard-nosed Bulldogs fans, it's hard to imagine any rugby league follower denying Williams' worth to the game.
The Roosters made the grand final in 2010 but unsavoury headlines were never far away.
However, under Williams, who in relative terms has been there five minutes, the foundation club has matured.
"I believe he's changed the culture of the club," said Coote, a dual premiership winner at the Roosters.
"To the extent where all the players are following him along and his preparation for a game and all of that is really first class.
"What Sonny Bill is doing with his preparation, I've always believed in that.
"I think our game is 90 per cent perspiration and 10 per cent ability. So if you've got the right preparation and psychologically you're thinking the right way (as a team), I think you're on the right track."
Williams' decision not to talk during grand final week has raised some eyebrows, but there's a fair argument to suggest he doesn't need to open his mouth to promote the game.
The 28-year-old has turned his public perception around through his actions on the field - and that was no small feat considering the circumstances in which he deserted his Bulldogs teammates.
"When he first came I didn't think that he was a great signing, but I've changed my opinion," Coote said.
"I did have a few reservations about him. I wasn't sure. I didn't know (about how) he'd left here and coming back I didn't know what he was going to be like.
"He'd played rugby union for five or six years or something so I didn't know what was left and what injuries he had.
"But he's a great player and he's done everything good."
Williams' former captain at the Bulldogs, Andrew Ryan, says he'd love to see the powerful second rower resist the All Blacks' temptation and stay in league.
Ryan said Trent Robinson and his coaching staff deserved credit, but that Williams has had a "huge" impact on the playing group.
"I've got no doubt Sonny has shown a lot of these guys the way," Ryan said.
"You can see the young Polynesian kids in their team and the young guys, they just watch what he does."