Olga Kosakiewicz (Ukrainian: ????? ?????????; 6 November 1915 – 1983) was a French theater actress.
She and her sister Wanda Kosakiewicz were born in Kiev as daughters of the Frenchwoman Marthe Kosakiewicz and the Belarusian emigrant from Kiev Victor Kosakiewicz.
From autumn 1934 to 1936 she studied medicine at the University of Rouen, then lived in Paris.
From 1934 to 1935 Beauvoir and from 1935 to 1937 Sartre had an affair with her.
Her irrepressible, rebellious character, characterized by emotional high and low, her authenticity and spontaneity charmed Sartre and Beauvoir.
She joined the circle of de Beauvoir and Jean-Paul Sartre.
Deirdre Bair's biography of Simone de Beauvoir examines this relationship.
Hazel Rowley also discusses it at length in her book about the relationship between Simone de Beauvoir and Jean-Paul Sartre.
In 1946 Olga married Jacques-Laurent Bost, a long-time lover of de Beauvoir.