Despite his advancing years, he has been playing his best rugby in the twilight of his career and picked up Grand Slams with Wales in 2005 and 2008 - the latter after Wales coach Warren Gatland enticed him out of international retirement.
His form for Wales and Cardiff Blues made him a certainty for a third tour and he was many people's tip for the Lions No7 Test jersey. But a shoulder injury picked up in the opening win over the Royal XV has kept him in the physio's room since then and forced him to miss the clash with the Free State Cheetahs last weekend.
His misfortune has given Munster and Ireland veteran David Wallace the chance to stake his claim for a place against the Springboks next week and he impressed in the record midweek win over the Sharks.
So now it is over to Williams to deliver against Western Province at Newlands this weekend and try to resurrect his claims for Test recognition.
"For a lot of us, Saturday's game is more or less like a final trial. We want to make it as hard as possible for Geech and the other coaches next week when they pick the Test team," said Williams.
"Geech made it clear from Day 1 that the Test side won't be selected until after Tuesday's match and that gives all of us something to aim for. We've got to go out on Saturday and raise the standard set by the team on Wednesday."
The Lions need a strong back row to challenge one of the strongest areas in the Springboks' game. Schalk Burger, Juan Smith and Pierre Spies have a massive reputation, and huge ability, and are just a few picks from an outstanding pool of back row talent in the South African squad.
Whoever plays at No 7 for the Lions in the series will be a critical figure and Wallace and Williams will have to be at the peak of their powers to match the Boks,
"I know I've probably lost a bit of ground because of my injury. It has been frustrating watching the guys play and train, but now I've got to make the most of my chance," said Williams..
"I haven't played in a trial match since Graham Henry had one when he was coach of Wales. I don't think there will be a danger of anyone trying too hard, it is just a question of playing your normal game
"I've trained all week and the shoulder has been as good as it has been for a long time. They hoped it would have cleared up for the Cheetahs match, but they put a cortisone injection in to get the inflammation down and that seems to have done the trick.
"I was alright during the game against the Royal XV, but on the day after the match I couldn't lift my arm above shoulder height. It's tough on tour when you are not playing and can't even train."
Look out for an explosive return at Newlands from the Welsh wizard.