They are bona fide legends of the game, tennis's very own Beauty and the Beast, the elegant Swiss arguably the greatest player ever and the physically indomitable Spaniard the undisputed claycourt king.
A pair of on-court dominators, off-court gentleman and sports ambassadors of the highest order.
Fierce rivals but also firm friends, Federer and Nadal shared a staggering 23 of 26 available majors from mid-2004 until the end of 2010.
Two grand slam gluttons feasting together like never seen before.
Yet it is now another player who stands on the brink of tennis immortality.
In 18 heady months, Novak Djokovic has spectacularly broken the seven-and-a-half-year Swiss-Spanish duopoly on the world No.1 ranking to establish himself as the pre-eminent force.
The 25-year-old Serb has transformed himself from one-slam wonder to a tennis super-Novak striving to join Australian Rod Laver as only the second man in the 45-year professional era to hold all four grand slam trophies simultaneously.
"His game has no weaknesses," Laver said this week in a French Open TV preview.
A maiden French Open triumph for Djokovic would complete a colossal feat that not even Federer and Nadal has managed.
Both tennis titans have had their own opportunities but, like Pete Sampras before them, each let a rare slice of history slip from their grasp.
Nadal twice denied Federer the non-calendar-year grand slam sweep with victories over the 16-times major champion in the 2006 and 2007 Roland Garros finals.
Then a hamstring strain and Spanish countryman David Ferrer conspired to thwart Nadal's quest for four straight slams in last year's Australian Open quarter-finals.
Sampras, the longest-serving men's world No.1 in history, is the only other player to have had a shot.
But with a career-long aversion to clay, Sampras came unstuck against fellow American Jim Courier in the 1994 quarters in Paris.
Now Djokovic, empowered by a gluten-free diet, unshakeable self-belief and the most destructive backhand in tennis, is dreaming of holding all four grand slam crowns, just as Laver did in 1969.
"I cannot say I'm not thinking about it," Djokovic said after losing to Nadal in Monday's Rome Masters final.
"There is the possibility to win four grand slams in a row. I will be preparing for this grand slam as I have all the others. It's a big event, it's two weeks' long and one of our most important tournaments.
"I want to deliver my best game. I'm feeling good on the court. I just need to make a few adjustments before Paris, but I'll be in top form."
Fighting words.
But to etch his name in sporting folklore Djokovic will likely need to deliver a superhuman performance in the French capital, where Nadal has lost only once in 46 matches - to big-hitting Swede Robin Soderling in 2009 a fortnight before abandoning his Wimbledon title defence with chronic knee soreness.
With an eighth title in Monte Carlo, seventh in Barcelona and sixth in Rome, Nadal has returned to his imperious claycourt best as he chases an all-time record seventh French Open crown.
"He is the best player in the world on this surface. He is always the favourite," Djokovic said.
But even Nadal conceded his success over Djokovic in Rome was huge psychologically.
"Winning is important. When you lose, you play with doubts," Nadal said. "This was an important match."
Nadal had succumbed to Djokovic in last year's Wimbledon and US Open finals, then again in their epic five-hour, 53-minute Australian Open decider in January.
Their series of showdowns marked the first time in the professional era that two men had clashed in three successive grand slam title matches.
Now Djokovic and Nadal are seeded to square off in the Roland Garros final for the first time.
Federer, though, is again standing in their way after the 2009 champion and five-time finalist intervened last year when he snapped Djokovic's 43-match winning streak in a French Open semifinal for the ages.
Barring a major upset, Nadal or Djokovic will again strike Federer in this year's semis, with the other projected to meet fourth seed Andy Murray for a place in the June 10 title match.
