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 December 1999 , Graf was named the greatest female tennis player of the 20th century by a panel of experts assembled by the Associated Press .