Steffi Graf plays tennis.
The Grand Slam tournaments , also called majors , are the four most-important annual tennis events . Stefanie Maria `` Steffi '' Graf ( [ ˈʃtɛfiː ˈgʁa : f ] ; born 14 June 1969 ) is a German former tennis player , who was ranked world No. 1 during her career . Furthermore , she is the only tennis player to have won each Grand Slam event at least four times . Graf is regarded by some to be the greatest female tennis player of all time . In 1999 Billie Jean King said `` Steffi is definitely the greatest women 's tennis player of all time '' .