Mona May Karff (20 October 1908 or 1911 or 20 October 1914 - 10 January 1998) was an American competitive chess player. Karff dominated U.S. women's chess in the 1940s and early 1950s and had an extended career. She held seven U.S. Women's Chess Champion titles and four consecutive U.S. Open titles.
She was born Mona May Ratner in Bessarabia, a province in Tsarist Russia. Sometime after the Bolshevik Revolution of 1917, her family moved to Tel-Aviv, in what was then Palestine. Her father, Aviv Ratner, a wealthy Jewish land-owner, had taught her to play chess when she was 9 years old. Because of her natural ability, she started playing in tournaments in Tel-Aviv and developed into a strong player.
In the 1930s, she moved to Boston. There she met and married her cousin, an attorney named Abraham S. Karff (15 March 1901 - 16 February 1995). The marriage was brief and, though she never remarried, her long-time romantic relationship with Edward Lasker (a five-time U.S. Chess Open Champion) was never a secret.
She played in three Women's World Chess Championships: 1937 Stockholm, playing for Palestine and placing sixth (won by Vera Menchik); 1939 Buenos Aires, playing for the U.S. and placing 5th (also won by Menchik); 1949 Moscow, playing for the U.S. (won by Lyudmila Rudenko). When FIDE established titles in 1950, Mona May Karff was one of four American women to receive the title of Woman International Master.
Karff, along with Gisela Kahn Gresser and Mary Bain, dominated U.S. women's chess in the 1940s and early 1950s. Mona May Karff won her first U.S. Women's Chess Champion title against Adele Rivero in 1938. She competed and won the title six more times, in 1941, 1943, 1946, 1948 (sharing it with Gresser), 1953 and in 1974 (at age 66). She also won four consecutive U.S. Open titles.
Mona May Karff was a private person; besides being a driving force in women's chess, she was a shrewd stock investor who was worth a small fortune. She spoke eight languages fluently and traveled extensively. As a lover of the arts, she spent a good portion of her fortune on modern art. She died in Manhattan on January 10, 1998.