JPR Williams' mutton chops, Jean-Pierre Rives' flowing blond locks, Jack Nowell's rat-tail.

And now Jack Goodhue's mullet has entered rugby's haircut hall of fame/shame.

The New Zealand centre has been a social media sensation at Japan 2019 with his retro look among the most distinctive at the tournament.

Among those to post about Goodhue's look was Jacinda Ardern as she congratulated the All Blacks on their quarter-final win over Ireland on Saturday.

"That's a brilliant win ... for the All Blacks and mullets everywhere," the New Zealand Prime Minister wrote on Instagram.

Goodhue, 24, had talked up the mullet's powers before the 46-14 last-eight victory as journalists questioned whether it would last the tournament.

"I'm not getting rid of the mullet," he said, adding jokingly that "there's actually scientific evidence that shows it makes me faster. It was done at Harvard, I think."

Ardern's admiring post only confirms Goodhue's claim from back in July that his haircut had been given the official seal of approval.

However there are signs that support from within the All Blacks dressing room is waning.

Goodhue's is the last mullet surviving after an outbreak of 'business-on-top-party-at-the-back' styles among the defending champions.

A core group of Brodie Retallick, Sam Cane and Liam Squire instigated the mullet growing last year, with star fly-half Beauden Barrett and brother Jordie also getting involved.

All have now gone back to something more conventional.

And so might Goodhue before the end of the year, with his wedding coming up around Christmas.

"Will I keep my mullet for the wedding? That'll be revealed on the day," Jack said in a joint interview with fiancee Sophia Eblett in Women's Day last month.

"It's become bigger than me and who am I to take away the inspiration it's given a few kids? But it might get shaved off in the middle of the night by Soph, so we'll see."