Martina Navratilova (born October 18, 1956, in Prague, Czechoslovakia) is a former World No. 1 woman tennis player. Billie Jean King said about Navratilova in 2006, "She's the greatest singles, doubles and mixed doubles player who's ever lived." Tennis writer Steve Flink, in his book The Greatest Tennis Matches of the Twentieth Century, named her as the second best female player of the 20th century, directly behind Steffi Graf. Tennis magazine has selected her as the greatest female tennis player for the years 1965 through 2005 and ESPN.com ranks her as 19th on the list of the 20th century's hundred greatest athletes. She won 18 Grand Slam singles titles, 31 Grand Slam women's doubles titles (an all-time record), and 10 Grand Slam mixed doubles titles. She reached the Wimbledon singles final 12 times, including 9 consecutive years from 1982 through 1990, and won the women's singles title at Wimbledon a record 9 times. She and King each won 20 Wimbledon titles, an all-time record. Navratilova is one of just three women to have accomplished a career Grand Slam in singles, women's doubles, and mixed doubles (called the Grand Slam "boxed set"). She holds the open era record for most singles and doubles tournament wins (167 and 177 titles respectively). She also recorded the longest winning streak in tennis history (74 matches in a row) and three of the six longest winning streaks in women's tennis history. Navratilova, Margaret Court, and Maureen Connolly Brinker share the record for the most consecutive Grand Slam singles titles (six). Navratilova reached 11 consecutive Grand Slam singles finals, second all-time to Steffi Graf's 13. In women's doubles, Navratilova and Pam Shriver won 109 consecutive matches and won all four Grand Slam titles in 1984. They also tied Louise Brough Clapp's and Margaret Osborne duPont's record of 20 Grand Slam women's doubles titles as a team.

Originally from the former Czechoslovakia, she lost her citizenship when she defected to the United States in 1975 at the age of 18, and became a U.S. citizen in 1981. Partially in protest of the policies of the Bush Administration she requested and received Czech citizenship on January 9, 2008. She has not renounced her American citizenship.