Simone de Beauvoir, a pivotal feminist philosopher, is recognized for her influential 1949 book, 'The Second Sex.' This foundational text challenged traditional notions of femininity as a social construct, arguing against biological determinism dictating women's destiny. Despite initial controversy and being placed on the Vatican's prohibited books list, her work inspired the second wave of feminism and activists like Betty Friedan. Beauvoir also advocated for legal changes, co-authoring the 1971 Manifesto of the 343, which called for abortion legalization and contraception access in France.