Sartre was a writer and existentialist following World War II. At the heart of his philosophy is a deep yearning for freedom and a concomitant sense of responsibility. While one is never free of their situation, Sartre felt, "in the end one is always responsible for what is made of one."
Sartre studied Husserl as a student, and was fasscinated by phenomenology. Some of his works from this period include The Imagination(1936), and The Transcendence of the Ego(1937). He discusses his ideas about the self in this period of his works, insisting that the self is not merely self-consciousness, but that it is out in the world.
In 1943 Sartre published Being and Nothingness, perhaps his most influential work. In it he states that consciousness is nothing, but that the self is on a journey to being something.
His later works include many plays, but most notably Critique of Dialectical Reason(1958-59), where he turns more toward politics, and Marxism.