Simone de Beauvoir was a French existentialist philosopher, writer, and social theorist who laid the foundation for second-wave feminism. Her 1949 masterpiece, 'The Second Sex,' offered a detailed analysis of women's oppression and the social construction of gender. She famously wrote, 'One is not born, but rather becomes, a woman,' arguing that femininity is an artificial construct imposed by a patriarchal society rather than a biological destiny. As a key figure in the existentialist movement alongside Jean-Paul Sartre, she explored themes of freedom, responsibility, and the 'other.' Her work challenged traditional marriage and family structures, advocating for women's economic and intellectual independence. She remains a seminal figure in both philosophy and women's studies, influencing gender theory for generations.