Simone de Beauvoir was a French philosopher, writer, and feminist known for her groundbreaking work in existentialism and feminist theory. Her most famous book, The Second Sex, explores the construction of women's oppression and is considered a foundational text in feminist literature. Beauvoir's ideas challenged traditional gender roles and emphasized the importance of personal freedom and choice. She famously stated, "One is not born, but rather becomes, a woman," highlighting the social constructs surrounding gender identity. Her influence extends beyond philosophy into literature and social activism, making her a pivotal figure in 20th-century thought.