Joseph Kavanagh is the protagonist of the novel. He is a dynamic character in that he changes from beginning to end. At the novel’s start, he is a complacent young man who aspires to climb the hierarchy of the closed society behind the Wall. However, he ends up finding meaning in living in the present and in relationships with others. As a Defender, Joseph is alienated from everyone. He feels angry and unhappy around his parents because he holds their generation responsible for climate change. He feels contempt for politicians who support the decision to maintain the Wall, and he sees civilians as people incapable of understanding the reality of life on the Wall.

His character first evolves as he begins to feel a sense of camaraderie with his fellow Defenders, who understand how harsh, boring, and potentially lethal life can be on the Wall. He goes from trying to comprehend the Wall by composing poetry about it, to accepting it as a given in his life. He fully accepts his identity as a Defender when he goes on a camping trip with several other Defenders, and after political leadership recognizes him for being wounded during an attack on the Wall.