Simone de Beauvoir was a French writer and philosopher who was heavily influenced by existentialism and Jean-Paul Sartre. She wrote The Second Sex in 1949, which argued that women are socially constructed as the "other" in a patriarchal society, and that this socialization is the root cause of women's oppression, not their biology. De Beauvoir asserted that one is not born a woman but becomes one, and that both individual and social change are needed for women's liberation.