Warburton was forced to announce his retirement from all rugby on Wednesday after failing to recover fully from neck and knee surgery.
And Williams believes the two time British & Irish Lions captain’s achievements during his career puts him at the top of the pile.
“Sam will go down as arguably the greatest flanker Wales have ever had,” said Williams.
“He can be so proud of what he’s achieved. People forget he played both six and seven and he’s right up there for me at the top table of anyone to have ever played the international game from any country.
“The shame for me is that there was probably more to come from him, but Sam was a Test match animal who always delivered in the big games. I’m down in the bargain basement of Welsh flankers after Sam’s announcement!
“For Sam it was always going to be a struggle to get back to the levels you have to get to after so long out of the game. He’s been used to coming back from injuries before and he’s spent his entire career doing it, so this is not something he would have taken lightly.
“He knows his body inside out and feels this is just one step too far.”
It is hard to isolate a single moment to define Warburton, especially considering he won a Grand Slam, Six Nations and became the most successful Lions captain in history during an illustrious career.
But there is one incident which sticks out in Williams’ memory.
“There’s one tackle which stood out for me,” he said. “It was on Manu Tuilagi in 2012 against England at Twickenham. We won the Grand Slam that year.
“Manu was in full flow and three metres from the line and he’s a huge unit who is virtually unstoppable from that distance. It was one of the best tackles I’ve ever seen.
“It wasn’t one of the most physical hits you’ll see, the sort of one everyone remembers, but it was just incredible. The decision to go low and have the ability to pull it off was phenomenal for me.
“Sam had so many great games, but that one moment stood out for me and it helped Wales win the Grand Slam.”
But according to Williams it is Warburton’s humble nature and his leadership ability which sets him apart from his peers.
“There are a few players you play with who you’ve got something on, but not Sam!,” said the 100-cap flanker.
“I know it’s been said a million times, but for me it’s about how he hasn’t changed a bit. He’s still the same guy now as he was when he was an 18-year-old academy player.
“He’s exactly the same bloke and it was a privilege to get to know him.”
