The Cappamore farmer, one of the five players who made their senior debuts against Scotland in February 2000, has answered 'Ireland's Call' time and time again.
The following statistic just sums up how important a member of the Irish team he is - 85 of his 89 Tests for Ireland have been as a starting player.
Hayes, who turned 35 last November, was ever-present during Ireland's Triple Crown-winning campaigns of 2004, 2006 and 2007 and memorably scored his second and last try for Ireland against Scotland at Murrayfield in 2005, swamped by his team-mates in the celebrations.
He always takes on a heavy workload, reliable and honest in the scrum, heroic at times as a lineout lifter and his efforts in the loose often go unseen. At anthem time, especially at Croke Park, his face can be a picture as he fights back the tears.
A two-time Heineken Cup winner with Munster, Hayes is just two European matches away from breaking Anthony Foley's 86-match caps record in the Heineken Cup.
Commenting this week at the team hotel, Ireland coach Declan Kidney, who shared those European successes with Hayes, spoke of his admiration for Ireland's most-capped prop.
"Everybody says tighthead is the cornerstone and I think no more so than John. To amass 90 caps is a phenomenal record and a testament to his professionalism and the way he's gone about it," he said.
"If I was to really say what I think of John, we'd be here another 20 minutes and he probably wouldn't thank me for it.
"(Saturday is) another milestone and please God he'll have another few more after that.
"I'm delighted for him and his family. Knowing John all he'll want to do is to get a result out of this one - that will be the best way he'll remember it."
Hayes signed a contract extension with Munster last November which will keep him with the province until 2010.