Steffi Graf was ranked No.1 in the world during World War II.
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 . World War II ( often abbreviated to WWII or WW2 ) , also known as the Second World War , was a global war that lasted from 1939 to 1945 , although related conflicts began earlier .