Frederick Engels completed volume 2 of Das Kapital after Marx's death, and wrote The Origin of the Family, Private Property, and the State in 1884. His work is the basis for much of the history in The Second Sex.
The influence of Heidegger's notion of "authenticity," the individual's positive engagement with the world by heeding "a call of conscious," operates throughout Beauvoir's appreciation for transcendence as an ethical principle.
Merleau-Ponty's work in perception, although grounded in phenomenology as a method, went beyond it in his focus in bodily behavior as an original source of knowledge. Intensely political and a Marxist, he broke with Sartre in a disagreement over the Korean War.
Sartre was a Marxist intellectual whose radical life style included his rejection of the Nobel Prize in Literature in 1964 and a much-scrutinized open relationship with Simone de Beauvoir. He was Beauvoir's closest associate and intellectual soul mate. He was also her critic.
Lévi-Strauss's work in structuralism influenced not only his field, but provided a methodology for generations of scholars in philosophy, comparative religion, literature, and film. His work in anthropology influenced Beauvoir.