Sartre as the narrator
He is the narrator of this piece of work and shares his views of how belief in Existentialism can lead to a happier and wholly fulfilling life. He argues that all people simply exist before they take on any deeper meaning. The essence of their being comes later on, with their actions and behavior through the life they lead. He urges the need for people to realize that their actions influence more than just themselves, but have a greater domino effect on humanity as a whole.
Man
Mankind as a whole is a character in this work as they are the main target of existentialism as a way of life. Indeed, Sartre argues that man is not truly special at birth, and that the qualities of the self come with their behaviors and actions in life. By giving us the chance to build our own "essence", man is truly the definition of free will.