The following is a list of the men who have won the most all-time Grand Slam singles titles in tennis since the Open Era began in 1968. The Open Era began when professional tennis players were finally allowed to compete at the Grand Slam events. Prior to the Open Era, only amateurs could compete.
I've been playing tennis since I could hold a racket in my hands over four decades ago. I've been following tennis for almost as long. I've watched all of these great champions at almost all the Grand Slam events they played in.
Tennis players who have won the most Grand Slam singles titles (Men)
1. Roger Federer - 17
In his remarkable career, Roger Federer has won 17 Grand Slam singles titles. The most in the Open Era (for men). Federer has won seven times at Wimbledon (2003-07, 2009, 2012), five times at the U.S. Open (consecutively from 2004-2008), four Australian Opens (2004, 2006, 2007, 2010) and one French Open (2009).
Roger Federer is now 33 years old. His last Grand Slam title was at Wimbledon in 2012. Can he win any more? Probably not, but he's been such a great champion you cannot totally rule him out.
T-2. Rafael Nadal - 14
Rafael Nadal is tied for the second most Grand Slam singles titles in tennis history (men) with 14. Nadal has won once at the Australian Open (2009), twice each at Wimbledon (2008, 2010) and the U.S. Open (2010, 2013), and a record nine times at the French Open (2005-08, 2010-2014).
Not even 30 years old yet (he's 28), Rafael Nadal will likely win even more Grand Slam singles titles. I would say he has a pretty good chance to reach and possibly even surpass Roger Federer, especially because of his dominance on clay at the French Open.
T-2. Pete Sampras - 14
With 14 Grand Slam singles titles, Pete Sampras is tied for second place with Rafael Nadal. Pete Sampras won seven times at Wimbledon (1993-95, 1997-2000), five times at the U.S. Open (1990, 1993, 1995, 1996, 2002), and twice at the Australian Open (1994, 1997).
Pete's power game did not translate well on the clay surface at Roland Garros. The best he ever did at the French Open was reach the semis in 1996.
4. Bjorn Borg - 11
Bjorn Borg won six times at the French Open (1974, 1975, 1978-81), and five consecutive times at Wimbledon (1976-1980) for 11 Grand Slam singles titles. Borg reached the finals of the U.S. Open four times, but lost each time. He only played at the Australian Open once in 1974, and lost in the third round.
Many players skipped the Australian Open in Borg's day. Had Bjorn Borg played the Australian Open regularly there is little doubt he would have won more Grand Slam titles.
T-5. Jimmy Connors - 8
Jimmy Connors won the U.S. open five times (1974, 1976, 1978 1982, 1983), Wimbledon twice (1974, 1982), and the Australian Open once (1974). Connors only played in the Australian Open twice, and he skipped the French Open at the height of his career from 1974 to 1978 due to a conflict with World Team Tennis.
Had Jimmy Connors played in Australia more often, and not skipped the French Open for five years during his prime, he would probably have won at least a half dozen or so more Grand Slam singles titles, and probably have a career Grand Slam in tennis.
T-5. Ivan Lendl - 8
Ivan Lendl won the U.S. Open (1985-1987) and the French Open (1984, 1986, 1987) three times each. He also won the Australian Open twice (1989, 1990), but he never won a Wimbledon title in 14 tries.
T-5. Andre Agassi - 8
Andre Agassi won the Australian Open four times (1995, 2000, 2001, 2003), the U.S. Open twice (1994, 1999), and won Wimbledon (1992) and the French Open (1999) once each. He would have won more titles if not for the presence of Pete Sampras.
Agassi faced Sampras five times in Grand Slam finals and went 1-4. At one point early in their careers, Andre Agassi had said he felt sorry for Pete Sampras because Sampras would never make it as a pro tennis player.
T-8. John McEnroe - 7
John McEnroe won seven Grand Slam singles titles in his career (kicking and screaming the whole time). McEnroe won four U.S. Opens (1979-81, 1984), and three Wimbledon titles (1981, 1983, 1984).
In five tries at the Australian Open the best John McEnroe managed was the semis. He did a little better at the French Open, making the finals once (1984) in 10 tries.
T-8. Mats Wilander - 7
Mats Wilander won the Australian Open (1983, 1984, 1988) and French Open (1982, 1985, 1988) three times each and the U.S. Open once (1988). He never got past the quarterfinals at Wimbledon. Wilander retired from the game in 1996, after testing positive at the French Open for drugs.
Mats Wilander now lives in Idaho, where the climate benefits his son Erik, who suffers from a connective tissue disorder. Wilander also travels around from time-to-time in an RV, and he will come to your home for personal tennis lessons (he's Swedish).