The holy grail of professional tennis is, without question, the calendar Grand Slam.
In this sport, a calendar Grand Slam is achieved when a player wins four consecutive Grand Slam events in the same calendar year. Although they have, at times, gone by different names, these four tournaments are now best known as the Australian Open, the French Open, Wimbledon and the US Open.
Winning even one of these tournaments in a year is a coveted achievement, but winning all four in a row instantly transforms a player into a living legend.
In the history of tennis, only five players have won the calendar Grand Slam. On the men's side of the game, there are two who can claim this achievement: Don Budge (1938) and Rod Laver (1962 and 1969).
For the women, there are three players who have achieved this great milestone: Maureen Connolly Brinker (1953), Margaret Court (1970) and Steffi Graf (1988).
The fact that only five players have achieved this feat in a set of tournaments originating over 100 years ago speaks volumes to the degree of difficulty involved.
When looking at the modern era of the sport, the list of calendar Grand Slam champions becomes even more exclusive. Tennis has several clear demarcations in its history, attributable to differences in the nature of the professional tour and eligibility/surface aspects of the tournaments we now refer to as Grand Slams.
Notably, prior to 1968 only amateurs could enter the Grand Slam tournaments. This was changed in 1968, after which both professionals and amateurs could compete for the Australian Open, the French Open, Wimbledon and the US Open.
While this was an important change, there were still several important aspects of even this so-called "Open Era" that differ from today's modern era. Most importantly, from the start of the Open Era through 1977, there were still only two unique surfaces on which the four Grand Slams were contested: grass and clay.
Of the four, the only tournament not using grass at the start of the Open Era was the French Open.
The introduction of a third unique playing surface didn't occur in Grand Slam tennis until 1978, when the US Open changed to hard court. It wasn't until 1988 that the Australian Open surface also changed from grass to hard court (albeit a slightly different type than the US Open).
It could be said that 1978 might be the best designation for the start of the modern era in tennis, because having at least three fundamentally different Grand Slam surfaces most closely resembles today's game.
These nuances, when applied to the calendar Grand Slam winners, create some interesting revelations. Using the surface change at the US Open as the cutoff, there has only been one winner of the calendar Grand Slam in the modern era: Steffi Graf.
Ultimately, that makes one female winner and zero male winners of the calendar Grand Slam over that time. Given that the original number was five, and included both sexes, the introduction of a third unique surface to Grand Slam tennis is arguably a critical development in the sport's history.
How many years will it be until the next Calendar Slam is completed?
The remote chance of winning the calendar Grand Slam during this new era is put in starker perspective when one considers that even winning three consecutive Slams has been extremely rare.
In the modern era, there have been three women and one man to win three consecutive Grand Slam events in a single calendar year. These players include Martina Navratilova (1984), Steffi Graf (1993, 1995, 1996), Serena Williams (2002) and Rafael Nadal (2010).
Interestingly, in each of those instances the player did so by winning the three consecutive Slams on three different surfaces. And since 1988, because of the configuration of the tournaments and their surfaces, winning three straight Slams in a calendar year must be done on three different surfaces.
Best described as the "Surface Slam," the notion of adapting and mastering grass, clay and hard courts in the same calendar year is mind boggling. To think only a single male player has achieved this result in the entire history of tennis is a tribute to the difficulty involved.
The difficulty factor of the mark is further supported by other facts in tennis history. From 1978-87, a player could win three Slams on three different surfaces through two different combinations: in non-consecutive order (Australian, grass; French, clay; US Open, hard court) and in consecutive order (French, clay; Wimbledon, grass; US Open, hard court). This was due to the fact that the Australian and Wimbledon were both played on grass for those years.
However, not one player did so non-consecutively during this period. Suggesting that even with the help of a longer preparation period, players during this window still could not adapt and find a way to complete the trifecta in this manner.
The sole player to achieve the mark between 1978-87, Martina Navratilova, did it the hard way - winning the last three Slams of the '84 season in a row.
Even expanding the criteria doesn't increase the number of players that have been able to conquer three different surfaces in immediate succession. If you include consecutive tournaments falling across two calendar years from 1978-87 there is still not a single instance of a player winning on all three surfaces consecutively.
Since 1988, the Surface Slam can only be achieved by consecutive combinations: by starting with the Australian Open and ending with Wimbledon, or by starting with the French Open and ending with the US Open.
Notably, each of the three players to achieve this since that time (Graf, Williams and Nadal) ran the same gauntlet as Navratilova, winning the last three Slams of the calendar year. The fact that both hard court tournaments now bookend the Slam season also makes it impossible for a player to win on three consecutive surfaces over adjacent calendar years, making that analysis moot.
The result is that five individuals have won the Calendar Grand Slam, while four have won the Surface Slam. Curiously, however, there have been six instances of each accomplishment. Making the Surface Slam nearly as rare as the Calendar Slam, albeit in a somewhat shorter period of time.
What can be gleaned from this analysis is that winning the Surface Slam in today's game is an extremely tall order. And tacking on a fourth Slam during the same calendar year must be considered a near heroic effort. The great Rod Laver, the only person to win two calendar Slams, seems to support this theory, telling Greg Garber at ESPN.com: "Look at the depth, the talent and the surfaces. In the 60s, they were playing three of the majors on grass and one on clay. It wasn't as tough for me."
Going forward, The Australian Open and the French Open should therefore have an added gravity for players and fans alike. Winning the title at the former and/or latter punches a bonus ticket. That ticket allows for the ability to compete for a special place in history, with possible admission into an ultra-exclusive club hanging in the balance.
It's clear that when another player does win two consecutive Slams toward the front-end of the calendar year, it would be highly advisable to monitor the next stage of their progress with meticulous care. You never know when you might see it again.