In this series we have asked our writers to recall their favourite sporting rivalries that have brought colour and drama to the games we love.
Brian O'Driscoll and Tana Umaga may only have faced each other for two games and 40 seconds of a third, yet it was enough for the legendary centres to create a bitter feud, the likes of which rugby had never seen before.
By the time the Lions arrived at the first Test of the 2005 New Zealand tour, O'Driscoll had forged a reputation which ensured he was spoken about in the same conversation as the world's best, including Umaga.
Four years earlier, the pair had come face-to-face in Dublin for the first time. O'Driscoll was very much the new kid on the block and at 21 was seen as the next big thing.
Umaga, on the other hand, was five years older and had already established himself as a ferocious midfielder who could do it all.
You can understand then, if the Kiwi wanted to stamp his authority on proceedings early on, but when he looked to make a strong carry down O'Driscoll's channel, Umaga knocked on, much to the chagrin of the Lansdowne Road crowd.
From the resulting scrum, O'Driscoll demonstrated his burgeoning class with a vicious step off his right, which left Umaga tied up in knots and grasping at thin air.
Ireland would soon score the game's first try on the back of O'Driscoll's break. The apprentice had firmly laid down the challenge to the master.
They didn't have to wait long for their second meeting as a year later Ireland toured New Zealand with O'Driscoll and Umaga again pitted against each other. As was the case seven months earlier, Ireland left the win behind them, with O'Driscoll to the fore again.
For all of his trojan efforts, however, he had still failed to notch that elusive first victory over the All Blacks and Umaga, who missed the second Test in Auckland.
Despite boasting a 100 per cent winning record over O'Driscoll, Umaga had been exposed by the young pretender on a couple of occasions, so he clearly understood just how talented his rival was.
This summer marks the 15th anniversary since O'Driscoll faced the Haka out in front alongside Dwayne Peel, who was the youngest player on the team, before the Lions captain plucked a piece of grass from the turf and threw it towards the line of huddled black jerseys.
The intention was clear as the Lions accepted the challenge laid down to them. Did the All Blacks see it that way or did they interpret it as a mark of disrespect? Either way, the opening 40 seconds in Christchurch still stands alone as the most controversial start to a game ever.
Having conceded an early penalty, which Justin Marshall took a quick tap from, the Lions were immediately on the back foot.
The ball was moved wide to Umaga, who took one look down O'Driscoll's channel before deciding better on trucking it up through midfield, and passing to Leon MacDonald on his outside.
O'Driscoll tackled the All Blacks full-back to the deck, and as he went hunting for a turnover at the ensuing ruck, Jerry Collins flew in to clear him out. What happened next was a recklessly violent, and not to mention extremely dangerous, act of foul play that somehow went unpunished.
Keven Mealamu was first to have a cut, but when he failed to uproot O'Driscoll, Umaga was quickly on hand to finish the job as the pair viciously drove the Lions skipper into the ground head-first.
And thus, 'Speargate' was born.
O'Driscoll's shoulder popped and the dislocation not only ended his tour, but also cost him five months out of the game.
In keeping with the ugliness of the whole affair, the aftermath was just as distasteful as the All Blacks went on attack.
Head coach Graham Henry labelled the incident "ridiculous". Nothing to see here, move on. The disciplinary panel took the same perplexing view as Umaga and Mealamu bizarrely avoided suspension.
For Umaga's part, he claimed the tackle was "totally accidental, one of those things", while Mealamu called it a "typical rugby movement." Yep, the mind still boggles.
Umaga doubled down on the whole affair two years later when he branded O'Driscoll a "sook" (cry baby). O'Driscoll, naturally saw it differently, describing it as "deliberate foul play, dangerous, a cheap shot".
He would never get a chance to exact some sort of revenge in doing what he did best on the pitch, because, later that year, Umaga called time on his international career at just 32.