He is only the second person to represent New Zealand in rugby union after first playing for the country in rugby league, and is one of only 21 players to have won the Rugby World Cup twice
Williams began his career in rugby league, and has played as a second-row forward over eight seasons in three spells in the National Rugby League (NRL), with the Canterbury-Bankstown Bulldogs and Sydney Roosters.
First moving to rugby union in 2010 and played mainly as a centre for Toulon in France, Canterbury, Counties Manukau, the Crusaders, Chiefs and Blues in New Zealand and Panasonic Wild Knights in Japan
Winning 58 caps for New Zealand (the All Blacks), and was part of the teams that won the 2011 and 2015 World Cups
He also played rugby sevens for New Zealand, competing in the 2015–16 World Rugby Sevens Series and the 2016 Olympics
Williams has boxed professionally seven times, winning all of his heavyweight bouts. He was the New Zealand Professional Boxing Association (NZPBA) Heavyweight Champion and World Boxing Association (WBA) International Heavyweight Champion