Cronin: O'Connell getting better
Veteran lock O'Connell will equal Mick Galwey's record as Ireland's oldest captain of all time at exactly 35 years and 145 days at the Millennium Stadium on Saturday.
The Munster talisman will become just the fourth star to hit 100 Tests for Ireland, joining Brian O'Driscoll, Ronan O'Gara and John Hayes in the century club.
Leinster hooker Cronin hailed O'Connell's "intensity and physicality" as the crux of Ireland's relentless pursuit of ever-higher standards under taskmaster boss Joe Schmidt.
"It's a phenomenal achievement: I think he's getting better with it even as the years go on," said Cronin, as Ireland look to home in on a second Grand Slam in six years this weekend.
"But he's the kind of player that, whenever he's playing, he nearly makes you play better because that's the enthusiasm, the passion, the physicality that he brings.
"He kind of instils that in the players around him, it's great to play under him.
"He sets the standard and you've got to get up there with him.
"He'll demand it off you one way or another, so it's great to play with a person like that, because it raises your standards as well."
O'Connell will stride past a multitude of milestones in Cardiff this weekend, as he aims to mark his 50th Six Nations performance by setting Ireland a new winning Test run of 11 matches.
Wales and Scotland block Ireland's path to Grand Slam glory and a third career Six Nations crown for O'Connell.
As the teams complete preparations in the Millennium Stadium's bowels this weekend, O'Connell will launch into a trademark tub-thumping team talk.
Cronin acknowledged the legend around O'Connell bringing team-mates to tears with his unbridled pre-match passion - but admitted the Munster stalwart's rhetoric far more fearsome than emotive.
"I've nipped out a couple of times to dot the eyes during his talks!" joked Cronin of myths O'Connell can invoke raw emotions.
"No, but seriously, he scares me more than makes me cry to be honest with you.
"He brings a certain level, you see him doing it, his intensity, physicality, attention to detail.
"So when you see him doing that, you're saying to yourself 'I need to get to that as well'.
"If 15 or 23 lads get to that level, we're hard to beat.
"He's similar to Joe (Schmidt) in some ways.
"Paul isn't going to get to the heights of Test rugby that he has without hard work and accuracy.
"He's got great influence on the squad, the lads buy into that and he's fantastic to have around."