Williams, who was christened John James but known throughout the world of rugby by his initials, was one of the finest finishers the game has seen.
He scored 12 tries in 30 appearances for Wales and won Grand Slams in 1976 and 1978, as well as four Triple Crowns between 1976 and 1979.
He scored a try in Wales’ 28-6 win over Scotland in Cardiff in 1976 and repeated the feat a year later when he touched down in an 18-9 win at Murrayfield during a golden era for Welsh rugby.
Williams toured South Africa in 1974 and New Zealand in 1977 with the Lions and his try-scoring exploits put him into the tourists’ record books.
He equalled David Duckham’s record of six tries in a single Lions game during a 97-0 victory over South West Districts in 1974.
Williams scored four tries in the subsequent 3-0 Test series triumph against South Africa, becoming only the second Lions player to score two tries twice in a Test.
He scored another Test try in New Zealand three years later and his five-try Test haul is only second to Ireland’s Tony O’Reilly, who crossed six times during the Lions tours of 1955 and 1959.
As a sprinter Williams competed at the 1970 Commonwealth Games for Wales, but gave up athletics to focus on rugby.
His former club Llanelli said: “It is with great sadness that we hear of the passing of the great JJ Williams. We would like to extend our sincerest condolences to his family, friends and former teammates.”