They are the men who plot their side's course through a match. The scrum half and fly half, No. 9 and No. 10 or, if you're a New Zealander, a first five-eighth.
The half-backs provide the brains to the brawn smashing lumps out of each other all around them.
Their performances, above all others, can determine the outcome of a contest, and when their understanding is on a par with the 10 pairs we look at here, they can propel their sides to great heights.
There have been few more animated, characterful No. 9s than Troncon.
For a scrum half, he was a bull of a player, snapping and snarling behind that grizzled Italian forward pack.
Troncon kept the supply line flowing to his mate at No. 10 for nine years. Dominguez was a colossus of the European club game with a glittering career at Stade Francais.
In the blue of Italy, he was one of the stars responsible for catapulting the Azzurri into the Six Nations, and once there, he kicked the wining points that brought them their first, famous win over Scotland.
Two of Italy’s most famous rugby sons deserve their place on this list for their importance to a rugby nation they helped put on the big stage.
Argentina took the 2007 World Cup by storm when they rampaged their way to the semi-finals.
Behind an uncompromising pack, Agustin Pichot was the terrier-like scrum half who probed, prodded and pushed his side forwards, while the man at No. 10 had magic in his boots.
Juan Martin Hernandez was in the form of his life in 2007. His running, passing and kicking were on another level.
Their partnership was forged at club level with Stade Francais, and their understanding inspired the Pumas to a third-place finish, with wonderful displays in particular against Ireland in the pool stage and France in the playoff for that third spot.
At the 1987 World Cup, these two had the luxury of playing behind a dominant pack but still stood head and shoulders above all other 9/10 pairings.
Fox was the points machine, amassing 109 of them on their way to victory, while Kirk notched four tries throughout the competition.
Kirk also skippered the side in the absence of the injured Andy Dalton.
Dawson fought a long battle with Kyran Bracken for the English No. 9 jersey, winning the starting place for the crunch games in the 2003 World Cup.
His combination with Wilkinson kept the England machine rumbling forward.
Dawson was at the heart of the winning play in extra time, first making a dart from the base of a ruck that, for a split second, looked as though he would scamper to the line.
Then he delivered the pass two phases later that provided Wilkinson with the chance to drop the winning goal.
The one thing missing from the celebrated 9/10 partnership of Justin Marshall and Andrew Mehrtens was a World Cup win.
Marshall’s game was based on speed, sniping and a razor-sharp pass. The measured Mehrtens was a wonderful kicker, both at goal and from hand, and he had the poise and intuition to put the dazzling array of runners around him into spaces where they could best display their wares.
Ask Jonah Lomu, Jeff Wilson, Tana Umaga and Co. if they’d have been half the attacking unit without the fluid axis of Mehrtens and Marshall pulling the strings.
Their answer will be no, no and no again.
Together they helped return Canterbury to the top of the domestic scene in New Zealand and between them amassed 151 caps for the All Blacks.
Van der Westhuizen played like an extra back-row forward.
His size and strength made him a potent runner from the base of ruck or scrum. His trademark darts from these positions caused no end of problems for the opposition.
Behind all that power and pace, Stransky sat in his armchair and did his thing, which was knocking over points.
The No. 10, who went on to play for Leicester, did exactly that in the 1995 World Cup final, scoring all 15 of South Africa’s points.
Farr-Jones had snap and bite as a No. 9, seemingly able to bully and boss his opposite man at will. Lynagh, on the other hand, was as smooth and serene as they come.
Between them, there was no one to touch them in the 1991 World Cup.
Lynagh had the ability to ignite his potent back line but was also an accurate goal-kicker, nailing two penalties and a conversion to sink England in the final at Twickenham.
This pair were at the helm of the 1999 World Cup-winning side and then masterminded the downfall of the 2001 British and Irish Lions.
Gregan’s game management, intelligence and sharp pass epitomized the side’s innovative way of playing under Rod Macqueen.
The leggy Larkham at fly half always appeared to have all the time in the world once his mate had delivered him the ball.
They were sublime in Australia’s run to that 1999 final in which they demolished France.
If you know only the tiniest piece of rugby history, there is a strong chance these two are at the centre of it.
In 1973, The Barbarians played the All Blacks in Cardiff. Early in the match, the Baa Baas attacked from deep, a move launched by Phil Bennett with two of the most outrageous sidesteps ever seen on a rugby field.
It was finished by his partner in crime Edwards, who latched on to the final pass of a move that set him free down the left flank to finish off the greatest try ever scored.
If you need further evidence of this pair’s brilliance, it is there in their record as a pair for Wales, and in their partnership at the fulcrum of the 1974 Lions test side that triumphed in South Africa.
Edwards and John forged their understanding as club mates at Cardiff, where they were inseparable.
Edwards, who was voted by readers of Rugby World magazine as the greatest player of all time in 2007, had pace to burn, a pass like a bullet and a wonderful understanding of the game.
Outside him, the man they called the King.
After his arrival at Cardiff, the pair were picked for the Lions tour to South Africa in 1968 and started the first test, only for John to break his collarbone.
Three years later, they were in harness again for the Lions’ series victory in New Zealand, having already sealed Wales’ first Grand Slam since 1952.