Most people consider either Roger Federer or Rod Laver the greatest tennis player of all time, with a few outliers mentioning Bjorn Borg, Rafael Nadal or Pete Sampras. 

But let's make it narrower and look at the greatest clay-court players of all time, despite the difficulty of comparing players from different eras.

The criteria for my rankings are the following: French Open finals reached; French Open titles won; titles won on clay; strong or weak contemporaries or injury problems.

Without further ado, here are the five best clay-court players.

Honorable Mentions: Guillermo Vilas and Gustavo Kuerten

Guillermo Vilas

French Open Finals Reached/French Open Titles: 4/1 (Won in 1977)

Number of Clay Titles Won: 46

The Argentine, who played between 1969 and 1992, pounded American Brian Gottfried in the 1977 French Open final 6-0, 6-3, 6-0 for his only Roland Garros title. In his other three French Open finals, he lost to Bjorn Borg twice and Mats Wilander once.

However, he does hold one of the most most remarkable feats ever on clay: Vilas won 53 consecutive matches on clay in 1977, starting with the French Open in May and not ending until the Aix-en-Provence tournament in September. (That was the record for a long time, until Rafael Nadal smashed it with 81 straight clay wins.)

Gustavo Kuerten

French Open Finals Reached/French Open TItles: 3/3 (Won in 1997, 2000, 2001)

Number of Clay Titles Won: 14

"Guga" has recently been inducted into the Tennis Hall of Fame, and it wouldn't have been possible had the Brazilian not won three French Open titles, his only Grand Slams.

He beat Sergi Bruguera, Magnus Norman and Alex Corretja in 1997, 2000 and 2001 in his only three Roland Garros finals. When he won it in 1997, Kuerten became the first Brazilian to win a Grand Slam singles title in the Open Era.

5. Roger Federer

French Open Finals Reached/French Open Titles: 5/1 (Won in 2009)

Clay Titles: 10

Yes, many people consider Roger Federer the greatest tennis player of all time, despite his Slam count featuring only one French Open title.

This is where the subjective part of the criteria comes into play.

We have to take into account that Federer was a contemporary of Rafael Nadal (who will unsurprisingly be featured later in this list), winner of seven French Opens. 

It is impressive that Federer was able to reach the Roland Garros final six times, winning it over Robin Soderling in 2009. The Swiss Maestro has lost five times to Nadal in Paris, four times in the final (2006, 2007, 2008, 2011) and once in the semifinals (2005).

This being said, losing to the same person over and over again while beating almost everyone else (except when he was much younger) has to be taken into consideration. Federer's record at the French Open is 54-13, which is a winning percentage of 80.6.

4. Mats Wilander

French Open Finals Reached/French Open Titles: 5/3 (Won in 1982, 1985, 1988)

Clay Titles: 20

Mats Wilander is one of only two players to win the French Open on the first try. In 1982, Wilander came into Roland Garros unseeded, but blazed his way to the final, where he beat No. 3 seed Guillermo Vilas in four sets.

The Swede won again in 1985, beating Ivan Lendl in the final. In 1988, he beat Frenchman Henri Leconte to win his third French Open title.

His two losses in the final in Paris were in 1983, to one-time French Open winner Yannick Noah of France, and in 1987 to Lendl, who avenged his 1985 final loss.

Wilander's presence in the International Tennis Federation Hall of Fame is in no small part due to his success on clay, especially at Roland Garros.

3. Ivan Lendl

French Open Finals Reached/French Open Titles: 5/3 (Won in 1984, 1986, 1987)

Clay Titles: 28

Lendl, who was originally Czechoslovakian but became a U.S. citizen later in his career, won eight major titles, three at Roland Garros.

His first French Open final was in 1981. He he took Bjorn Borg to five sets, but lost 6-1 in the deciding set.

Between 1984 and 1987, Lendl got to four straight French Open finals, winning three against John McEnroe, Swede Mikael Pernfors and Mats Wilander. However, in 1985, he lost to Wilander in the final in four sets.

This record of four consecutive French Open finals is matched by Rafael Nadal, Roger Federer and Bjorn Borg.

In 15 tries, Lendl reached five French Open finals, an impressive feat when one considers his strong contemporaries such as Borg, Wilander, McEnroe, Guillermo Vilas and Yannick Noah.

2. Bjorn Borg

French Open Finals Reached/French Open Titles: 6/6 (Won in 1974, 1975, 1978, 1979, 1980, 1981)

Clay Titles: 30

What is amazing about Bjorn Borg's career is that he retired at the age of 26, so all the achievements came in a short amount of time.

For example, Borg has six French Open titles, but he only played the French Open eight times, which gives him a success percentage of 75. He went 49-2 at Roland Garros (96.08 percent).

His only two losses in the French Open final, in 1973 and 1976, came against Italian Adrianno Panatta in the fourth round and the quarterfinals, respectively. Both losses were in four sets, and Panatta went on to win it in 1976.

In the 1978 French Open, Borg went 127-32 in games throughout the tournament, a winning percentage of almost 80. Between 1979 and 1981, Borg won 41 consecutive sets at the French Open, a record which no one has been able to match.

Borg's victims in the French Open finals were Manuel Orantes of Spain, Guillermo Vilas twice, Victor Pecci of Paraguay, American Vitas Gerulaitis and Ivan Lendl.

1. Rafael Nadal

French Open Finals Reached/French Open Titles: 7/7 (2005, 2006, 2007, 2008, 2010, 2011, 2012)

Clay Titles: 36

Rafa is the King of Clay. He has a perfect record in French Open finals, beating Mariano Puerta, Roger Federer four times, Robin Soderling and Novak Djokovic.

• Here is a list of clay-court achievements for Nadal:

• 31 consecutive match wins at the French Open

• 81 matches unbeaten on clay (the second most is 53)

• A record of 52-1 at Roland Garros (98.11 percent)

• Won 2 French Opens without losing a set

• Only person to win the Clay Slam (Monte Carlo, Rome, Madrid, French Open in one year)

Nadal is virtually unbeatable on clay. His only loss in Paris was to Robin Soderling when Rafa had tendinitis (but to be fair, the Swede played brilliantly).

Who knows how many more French Open titles Nadal will win?