Steffi Graf is not an athlete.
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 . In 1988 , she became the first and only tennis player ( male or female ) to achieve the Golden Slam by winning all four Grand Slam singles titles and the Olympic gold medal in the same calendar year . In 1999 Billie Jean King said `` Steffi is definitely the greatest women 's tennis player of all time '' .