Jean-Paul Charles Aymard Sartre (, US also ; French: [saʁtʁ]; 21 June 1905 – 15 April 1980) was a French playwright, novelist, screenwriter, political activist, biographer, and literary critic, as well as a leading figure in 20th-century French philosophy and Marxism. Sartre was one of the key figures in the philosophy of existentialism (and phenomenology). His work has influenced sociology, critical theory, post-colonial theory, and literary studies, and continues to do so. He was awarded the 1964 Nobel Prize in Literature despite attempting to refuse it, saying that he always declined official honors and that "a writer should not allow himself to be turned into an institution."

Sartre held an open relationship with prominent feminist and fellow existentialist philosopher Simone de Beauvoir. Together, Sartre and de Beauvoir challenged the cultural and social assumptions and expectations of their upbringings, which they considered bourgeois, in both lifestyles and thought. The conflict between oppressive, spiritually destructive conformity (mauvaise foi, literally, 'bad faith') and an "authentic" way of "being" became the dominant theme of Sartre's early work, a theme embodied in his principal philosophical work Being and Nothingness (L'Être et le Néant, 1943). Sartre's introduction to his philosophy is his work Existentialism Is a Humanism (L'existentialisme est un humanisme, 1946), originally presented as a lecture.