an advocate or follower of the doctrine that human beings are morally free, and responsible for making their own system of values in an otherwise meaningless universe; an existentialist.

the doctrine that concrete, individual existence takes precedence over abstract, conceptual essence and holds that human beings are totally free and responsible for their acts and that this responsibility is the source of their feelings of dread and anguish and also that it denies objective universal values and holding that a man must create values for himself through action and by living each moment to the full; existentialism.