Simone de Beauvoir was a French writer, philosopher, political activist, and feminist. She is best known for her 1949 treatise 'The Second Sex', which is considered a foundational text of contemporary feminism. De Beauvoir also wrote novels, essays, biographies, and monographs on philosophy, politics, and social issues. She was a lifelong companion of Jean-Paul Sartre, and their relationship had a significant influence on both their intellectual and personal lives.