William Marshall Mason (born 15 April 1980), also nicknamed "Big Willie", is a former professional rugby league footballer who played in the 2000s and 2010s.

An Australia and Tonga international and New South Wales State of Origin representative forward, he played in the National Rugby League for the Canterbury-Bankstown Bulldogs (with whom he won the 2004 Grand Final and Clive Churchill Medal), the Sydney Roosters, the North Queensland Cowboys, the Newcastle Knights and the Manly-Warringah Sea Eagles.

[4] During his career Mason was involved in a number of controversial off-field incidents which have received media publicity due to his high profile in the NRL.

After the 2000 season, Mason made his international debut for Tonga, his mother's country of origin, in the 2000 Rugby League World Cup played in Great Britain and Ireland.

[12] Mason forged another player's signature at an autograph event, and after a heavy drinking session with teammates, reportedly visited a brothel.

Also at the end of 2004, Mason played in Australia's win over the United States in an international rugby league friendly match at Philadelphia's Franklin Field but suffered a fractured ankle.

In June 2006, news speculation surfaced that Mason was considering joining the United States' National Football League (NFL), a childhood dream.

[17] In July it was confirmed the New York Giants had offered him the opportunity to trial with them after the Rugby League Tri-Nations series finished in November.

[20] Mason explained that his swearing was in response to the traditional Māori dance being performed by Brent Webb, an Indigenous Australian of Torres Strait Islander origin who became a New Zealand citizen.

[21] In December 2006 Mason took part in a trial with the New York Jets, but still maintained he would fulfil his contract with the Canterbury club until the end of the 2009 season.

I'm pretty sure I could settle in there if given the opportunity..."[23] However a Jets representative stated that Mason even being offered a contract was very unlikely, "I don't think they were even football drills, it was more of a visit.

The Jets coach Eric Mangini was impressed with Mason, saying "Willie is a guy that came to our attention, he is a pretty good rugby player, and it was just one of those opportunities we had, where we have to take a look at him.

"[24] Mason was selected to play for the Australian national team at second-row forward the 2007 ANZAC Test match victory against New Zealand.

On 31 October 2007 The Daily Telegraph reported that Mason wanted to leave the Bulldogs after an altercation with the club's CEO, Malcolm Noad.

[36] In February 2008, Mason and his new Roosters teammate Anthony Tupou were charged with urinating in a public place during a visit to Port Macquarie.

In September 2011, Mason signed a three-year contract with Hull Kingston Rovers, pending a successful working visa application.

[51] Six months into his contract, Hull KR were forced to release Mason as he was unable to obtain a Tongan passport that would have enabled him to come off their overseas quota.

The offence was in relation to Australia Day of that year where after a marathon drinking session, Mason drove to training, was pulled over by police and blew a blood alcohol reading of 0.09.

[57] On 28 October 2014, after a three-year stint with the Knights, Mason signed a one-year contract with the Manly Warringah Sea Eagles starting in 2015.

"[60] In 2018, Mason spoke to the media about his time at Manly in relation to the ongoing saga with the board infighting and coach Trent Barrett claiming the facilities at the club were not up to date.

[61] On 16 February 2016, Mason returned to the Super League with Catalans Dragons, signing a one-year contract starting effective immediately.

[68] In June 2018, Mason claimed that when he was at Manly that nobody wanted to play alongside teammate Daly Cherry-Evans and that he was the reason there was such a divide at the club.

[70] In September 2023, Mason publicly sledged some of the Newcastle players on his LEVELS podcast saying that the club had the “worst f**king spine in the league without Kalyn Ponga”.

After Newcastle were eliminated the following week by the New Zealand Warriors, Mason took to his social media account and wrote "There could not be a bigger hole that Tyson Gamble wants to crawl into right now.