With Ma'a Nonu having retired, the way has been paved for Williams to establish himself as the All Blacks' preferred second five-eighth and take ownership of a jersey he first wore in 2010.
Williams has previously signed only one-year deals but his certainty that he wants to win 50 test caps and be remembered as a great All Black is thought to have persuaded him to make a longer commitment.
By doing that, he was also able to benefit from the newly-signed broadcast deal. Williams, like all senior players in New Zealand, will enjoy a massively-improved pay deal as a result of the 100 per cent increase in TV income. He will also be allowed to box professionally as part of the deal.
WHY THE CHIEFS
The Chiefs were his rugby saviour and he feels a loyalty to them. Having initially played for the Crusaders when he arrived in New Zealand six years ago, Williams didn't settle well in Christchurch.
He wasn't warmly embraced by the Crusaders' senior All Blacks and when his coaching mentor, Wayne Smith, shifted to the Chiefs as technical director in 2012, Williams decided to follow him.
The shift paid immediate dividend as he struck a deadly partnership with first-five Aaron Cruden and formed a strong friendship with captain Liam Messam. The Chiefs won the title that year and Williams was instrumental in delivering it.
After he fulfilled what he said was a long-made commitment to return to the NRL in 2013 and 2014, Williams rejoined the Chiefs for the 2015 season and is technically available to them between sevens commitments.
WHY THE BLUES
But while he has loyalty to the Chiefs, he also has a strong relationship with Blues coach Tana Umaga who was at Toulon when Williams first defected from league.
Umaga, as a former world-class midfielder, had a major influence on Williams' early rugby development and the two are close.
Williams played for Umaga's Counties Manukau team in the ITM Cup when he returned from the Sydney Roosters in 2014.
He and his family are currently based in Auckland, the city in which he grew up before he left for Sydney in his mid-teens.
Snaring Williams would be a massive coup for the struggling Blues who are short of star quality and seemingly always miss out in any competitive process to sign leading talent. They made a bid to sign Damian McKenzie earlier this month but he rejected their offer to stay at the Chiefs and it confirmed the damaging perception that the best players don't want to head to Auckland.
Sonny Bill Williams
Age: 30
Height: 1.94m
Weight: 108kg
Caps: 33
Teams
2010: Canterbury
2011: Crusaders
2012 and 2015: Chiefs
2014: Counties Manukau
2010-12, 2014: All Blacks
2016: All Blacks Sevens
Test debut: November 6, 2010 v England at Twickenham
Test tries: 9