Brian O’Driscoll playfully jibed that the then 20-year-old, who secreted a wealth of mathematical information beneath his shaggy mop top, was more likely to forget lineout calls than nail them in his early incarnation as a fledgling international.

However, Henderson is no ordinary athlete, nor indeed human being.

With an uncommonly high IQ and EQ, he somehow successfully maintains the life balance denied to so many of his peers; he is just as happy gambolling around the house with his dogs than he is bulldozing Eben Etzebeth. It has not always been the case that the body and brain of Henderson were allies in forging the career of a now two-time Lion.

There was the slightest chance that his body’s momentary weakness might have made him doubly determined to maximise the strength of his brain and pursue a life away from the professional scene.

Perhaps his heart ultimately intervened; a child of the Academy club in North Belfast, it is hardly one of Ulster’s most renowned establishments but it is the club his father, Gordon, captained, and in which the family are steeped in long-lasting tradition.

Chris McCarey coached the Belfast Royal Academy team that reached the 2010 schools final and vividly recalls the setback that at once almost de-railed him as an athlete but also would come to define him as a person.

“He really didn’t stand out in school,” McCarey remembers. “He was on our team but not for one moment were you suspecting a future Lion in our midst.

“And then he missed an entire year in year 13 (equivalent to fifth year in the Republic). His knee kept locking and he had to have some cartilage removed.”

This physical intervention, combined with a laid-back attitude some might have twinned with laziness, might have convinced many, perhaps even the kid himself, that maybe flinging the discus, which he did quite well, might have served a better purpose.

Except when McCarey next clapped eyes on him, a feral beast, unleashed from lengthy hibernation, laid waste to the open prairies.

“We played Ballyclare and I still see it now. He caught the kick-off, then ran the entire length of the pitch. Eventually, eight guys pinned him down before the try-line. Eight of them!

“That was the moment I knew he would be something special. Before, he had been just another average player. Now this was different.

“Then there was a time against Inst (RBAI) in a third-round replay. We led all the way until they scored a penalty at the death.

“We kicked off for the last time and they received. All they had to do was get it out and off the field. But he single-handedly turned the ruck over like some kind of superhuman athlete. And we engineered a drop-goal.”

McCarey laughs at the memory of a school trip when the boy raised a teacher atop his head with just one arm. “He was a colossus.”

Not everyone agreed. Henderson never registered at age grade level for province or country.

“He just slipped through the net,” says Tommy Bowe. “He wasn’t one for ticking all the boxes, wouldn’t have been the most diligent, or the best time-keeper.”

So there were no Academies beating a path to his Craigavon front door. Heriot Watt university in Scotland had done so, however; they offered him actuarial studies. Henderson accepted. And then another invitation arrived. This time somebody in rugby had taken notice. A letter from Jonny Bell at the Ulster Academy joined the bulging inbox.

“Iain is very much his own man,” according to Bell, who seeks to downplay his role in applying the subtle pressure to re-route Henderson’s next career move.

“He is switched on. It’s less that I dissuaded him at all rather than the offer reinforced a few things. He makes his own decisions. He has his family who help him. Like any young kid, he had decisions to make. He’s smart. You can lend your thoughts to him but he’ll make his own mind up.

“At Ulster, we were keen to keep him and really try to show that we could work with him and invest in him. That’s the purpose of an Academy, to develop as a rugby person and as a person.”

Bowe had experienced something similar.

“Although it would have helped had I actually passed my exams! It was a dilemma, he could have gone to study. He wasn’t that enamoured by rugby because he wasn’t getting the love back.”

“He had very good options,” says McCarey. “He is an excellent mathematician, extremely bright. He was never single-minded about rugby. Rugby came upon him rather than him chasing rugby.”

When the Aviva Stadium re-opened in 2010, a mixed interprovincial clash featured Henderson; Bell pointed him out to Colin McEntee (now IRFU head of development).

Concerns were expressed about his lineout work. After 80 minutes they were forgotten about. “F**k me, this kid has something!”

The tactical rawness would soon dissipate but the physical prowess did not.

“I remember coming back from Wales,” says Bowe, ”and I was laughing at this kid on the sidelines, falling over himself trying to do the pre-season exercises, hair going everywhere. ‘You just wait, the S&C guy said. ‘He’s smashing records all over the place. He’s the real deal.’”

“He was a great athlete,” continues Bell, “but still pretty raw as you would be at that age in terms of rugby knowledge. We wanted to keep him in pathway and focus on him and devote a bit of time and attention to him. He had an intelligent, good rugby sense and he was powerful at that young age. He was going to get even better.

“He was always a laid-back individual – a man-child. He had this man strength physically. It didn’t look as if he could swat people off, but then he’d leg drive them.”

The sense that he was the man for the ‘big play’ rather than a ‘big player’ typified his character, not his commitment.

Coaches were often confounded by this dichotomy. Mike Ruddock had him in his 2012 U-20 World Cup final squad and saw both sides.

“I’d seen him at Ulster and it didn’t seem like he was that switched into it and there was a mixed vibe about him,” says. “I had him in a game against Italy and he came on after only two minutes. He didn’t play as well as he trained.

“He tells me, ‘I didn’t expect to go on that early’. I always remember that! I told him you always have to make an impact. That showed where he was in his head but he had so much promise.

“And then to attain the current degree of physicality is world-class from a lad who was perhaps not as quite in tune as he might have been.

“Now he is a leader. We always spoke to him about work-rate, that was a criticism of him, he was fits and starts and he just needed to get consistency,” adds McCarey.

Having spurned one road in the woods for another, Henderson never felt like losing his way; he was just a guy who always seemed to enjoy the journey rather than fretting about the destination, like so many addled colleagues.

In some ways, it was as if he were born in the wrong era. It is a tribute to him that he could thrive in any.

Which is why it took a while for both Ulster and Ireland to extract the optimum from him; in 2021, he is arguably at the peak of his formidable powers.

“There have been times we haven’t seen him at his best but not so lately,” says Bowe. “Seán O’Brien said it in his book. He doesn’t realise the potential he has.

“It comes down to him being a clever guy. I wouldn’t say he’s smug but he likes to show it, he needs to be challenged. Jono Gibbes, Steve Borthwick, Paul O’Connell, Rory Best, characters like these bring out the best in him if he gets a bit too relaxed.”

He has found the balance in more ways than one. “What he has achieved is unbelievable,” sums up Bell. “It’s down to ability but the amount of hard work and effort is so professional.

“He worked incredibly hard at his game. And his leadership has grown throughout the years. That is testament to his character.”

LIONS IN FOCUS

Name: Iain Henderson,
Ulster, Lock, Back-row
Age: 29
Height: 6ft 6in
Weight: 18st 4lb
Ireland caps (Points): 63 (25)
Form: Timed his run perfectly to reach the most sustained run of consistency in his career, emerging ahead of a once much-touted Irish rival, James Ryan.
Test chances: More than likely a non-starter given dearth of audition time and pronounced quality in his positions but, given his versatility, there is a good chance that his name will be inked on the bench from a long way out.