As of today (11th June 2012), there are 14 players that have won the Grand Slam, the four major tennis Championships - French Open, Australian Open, US Open and Wimbledon.

Rod Laver from Australia won the Grand Slam in 1962 as an amateur and then he won the four championship titles again in 1969 as a professional. This makes him the only male tennis player who has won the Grand Slam twice. Rod also has the most singles titles with a whopping 200 career titles.

Margaret Court is another Australian player who won the singles Grand Slam in 1970. She also won the mixed double Grand Slam in 1964 and 1965.

Female player Steffi Graf from Germany won the Grand Slam in 1988. In the same year, she also won the Olympic gold medal, which makes her the only tennis player who completed the Calendar Year Golden Slam.

For the whole list, check here.