Second-row Jones will win a record 130th cap for his country in Sunday's crunch Pool D game against Australia at Tokyo Stadium, 13 years after his debut.
"That's just incredible, to play for Wales for 13 years," said full-back Williams, who, against the Wallabies, notches his 60th appearance. "I've been here for seven years, and it feels like I've been here for ages, and it's almost double me.
"He's a great bloke and leads from the front. He speaks well, and does his talking on the pitch. He's a leader.
"He seems quite calm at the moment. He doesn't unleash the fury, not on me anyway. But then he's the skipper so he can do what he wants."
Jones, who also has nine caps for the British and Irish Lions, equalled Gethin Jenkins's Wales record in the opening match 43-14 victory over Georgia.
He won his first cap in Patagonia in 2006. Thirteen years later, @AlunWynJones will break the Welsh record when he wins his 130th cap in Tokyo at #RWC2019. Dyn hynod ysbrydoledig. pic.twitter.com/FVoafUtc5N— Welsh Rugby Union 🏉 (@WelshRugbyUnion) September 27, 2019
He will make his record appearance in a game that will help determine whether Wales can go all the way in the final campaign of coach Warren Gatland, pictured above with Jones.
"It's our biggest game. We've had a couple of tight games back at the Principality (Stadium) against them," said Williams.
"It has always been nip and tuck and we've always come away on the losing end, except for the autumn one last year.
"We've worked hard to get where we are and hopefully that will take us into the game. We have got a few tricks up our sleeve and as long as we stick to the process, we'll go well.
Ready to go
"If we're not at our best we're going to lose badly, but I'm pretty sure the boys are in a good place. It's been a good week and we're really ready to go.
"I am sure it is going to be hot out there so if the game does open up, then happy days."
Williams says there have been some clashes between the players as the intensity in training has increased this week, with some of those left out of the starting XV looking to make their mark.
"There was a bit of argy bargy but there's always argy bargy in rugby training.
"I wasn't leading it. I was out the way in the gym doing curls with the backs. We just left it to the forwards."