David Watkins, who played for Wales at rugby union and rugby league as well as for each sport's British and Irish Lions teams, has died at the age of 81.
He won 21 Wales union caps from 1963-67 and 16 more at league, adding six each for the Lions in the 15-a-side game and their league counterparts.
Watkins starred at stand-off in both codes.
The Rugby Football League said Watkins would "be remembered as one of the best cross-code converts from Wales".
The governing body added: "He became a key figure in a golden era for the Salford club, making more than 400 appearances for the Red Devils, and scoring almost 3,000 points as they were crowned champions twice in the space of three seasons in the mid-1970s."
Wales Rugby League said: "Dai, as he was affectionately known, is recognised as one of the greatest Welshmen to have ever pulled on a rugby shirt."
On social media, Newport RFC said: "We are extremely saddened to hear that David 'Dai' Watkins, one of the greatest players the club has ever produced, has passed away."
Watkins rose to prominence in Wales after joining Newport RFC in 1961, helping them famously beat New Zealand 3-0 in 1963.
In 1967, when moving to the professional ranks of rugby league at Salford for £16,000, Watkins was barred from playing union.
He went on to produce mesmerising performances for Salford, Wales and Great Britain before moving into coaching.
Watkins guided Great Britain to the 1977 World Cup final, in which they lost narrowly to Australia and went on to coach Wales, help found Cardiff Blue Dragons league team.
He returned to union as Newport team manager in 1992 before becoming chairman, the president.
Watkins' passing was announced shortly before Newport hosted Pontypool in the Welsh Premiership, with flags lowered to half mast in tribute.
Tributes also came from leading figures in both sports.
Ex-Wales and Great Britain forward Jim Mills posted on social media: "Heartbreaking news the legendary David (Dai) Watkins has passed away, a wonderful player in both codes of rugby, the only man to captain the Lions in RU & RL.
"Dai was such a lovely man and will be greatly missed. He will never be forgotten. My deepest sympathy to his wife Jane & family."
Regional team Dragons RFC, who are also based in Newport, wrote: "Our thoughts of us all @dragonsrugby and with everyone at @NewportRFC and the family of Dai Watkins."