Only five men have achieved golfing immortality by winning each of the four majors and completing the coveted Grand Slam.
Jack Nicklaus, Tiger Woods, Ben Hogan, Gary Player and Gene Sarazen stand alone among the pantheon of greats to have topped the leaderboard at The Open, the U.S. Open, the US PGA Championship and the Masters.
Arnold Palmer, Tom Watson and Walter Hagen are among the sport's legends to have accomplished three legs of the Slam – an impressive feat in itself.
Indeed, three active players are just one away and each is eyeing a different title. Rory McIlroy is missing a Masters, Jordan Spieth a PGA Championship and Phil Mickelson a U.S. Open.
For Mickelson, it is certainly not for want of trying – on six occasions he has finished second or tied second for a prize he so greatly craves.
It appeared as though his chances were waning as Father Time had seemingly caught up with a true great. But then, Mickelson upset all the odds to win a sixth career major and second PGA Championship at Kiawah Island last month at the age of 50, making him the oldest player to win a major tournament.
With renewed hope at finally claiming the missing piece of the puzzle, we assess the chances of Mickelson, Spieth and McIlroy in the race to complete the Grand Slam.
In terms of a straight race, you could argue that 'Lefty' is in pole position merely because his opportunity is next up.
Moreover, Mickelson has history at Torrey Pines – hosting the U.S. Open for the second time having last done so in 2008 – a venue where he is a three-time winner, albeit the last of those was in 2001.
But that in itself is testament to Mickelson's astonishing longevity, and he made a mockery of suggestions his major-contending days were over at Kiawah Island.
Still, to mix it at that sort of level in the 50s (Mickelson turns 51 on Wednesday) on a regular basis is tough. Indeed, the unexpected triumph was his only top-10 finish on the PGA Tour this season, while he ranks down at 167th for scoring average.
While he does impressively still average over 300 yards off the tee (302.8), in terms of fairway accuracy Mickelson is down at 199th (51.16 per cent), and a putting average of 1.791 would need to be improved to contend.
All in all, you would be a fool to say Mickelson cannot complete the Slam but, speaking pragmatically, even accounting for his PGA Championship heroics, it will take a monumental effort to go back-to-back in the majors this weekend.
A player of outrageous talent whose career in terms of majors has perhaps not quite hit the heights many tipped him to reach.
McIlroy has four to his name thus far, the last of which arrived at the 2014 US PGA Championship. At that stage, it appeared a question of how many he would win.
It has been a decidedly mixed bag since at the majors, and there is no doubt winning a green jacket is a prize McIlroy would crave above all others in his career.
There have been plenty of close calls at Augusta, where he has six top-10 finishes, and that does not include the 2011 tournament where McIlroy led heading into the final round before enduring an excruciating Sunday that saw him finish way down in 15th.
Once upon a time it would have sounded unthinkable McIlroy would never win a Masters. It's not as clear cut now perhaps, but there are many opportunities left for a player still only 32 years of age.
McIlroy has endured inconsistent form this season, but was a recent winner at the Wells Fargo in a sign that things are slowly starting to click back into place.
His scoring average of 70.363 is the 31st best on the PGA Tour this season, while he ranks tied 14th for top-10 finishes (five).
Only Bryson DeChambeau averages longer off the tee than McIlroy's 318.6 yards but he is way down in 173rd for driving accuracy, while a putting average of 1.740 is something he will be keen to improve.
Rory McIlroy will become the first European to win 3 different majors since The Masters was founded in 1934. pic.twitter.com/Bwov2zuIem— The Open (@TheOpen) July 20, 2014
One of the most pleasing aspects of recent months has been the resurgence of Spieth, who had slipped as low as 92nd in the world rankings having missed the cut at the Farmers Insurance Open earlier this year.
But eight top-10 finishes – including a win at the Valero Texas Open – has catapulted him back up to 23rd and many fancied him to complete the Slam at the PGA Championship.
Despite fleeting flashes of promise, Spieth could only finish down in 30th but crucially – much like McIlroy – time is on his side. Indeed, due to the early career success that has seen him become a three-time major victor, it is easy to forget he is only 27.
Prior to Mickelson's triumph last month, the smart money would have been on either McIlroy and Spieth to do the Slam first and perhaps it still is.
Indeed, Spieth probably remains a solid bet to deny Mickelson's own hopes this weekend. He is 21st for scoring average (70.178) and second only to Jon Rahm (10) for top-10 finishes with eight.
Not known as a particularly big hitter off the tee, Spieth is down at tied 83rd for driving distance (298.0) and 184th for driving accuracy but only nine players have a lower putting average than his 1.716.
In terms of immediate chances then, yes, of course Mickelson has the edge. But logic suggests that it will need a monumental effort for him to repeat what he did at Kiawah Island at Torrey Pines. McIlroy and Spieth can, theoretically at least, continue to compete at the top for the best part of the next two decades. If they do, both have ample opportunity to secure the Grand Slam. As for who does it first…well given the Masters is closer than the PGA then let's go with McIlroy. Check again next April!