The correct answer is "protagonist".
A protagonist is the leading character of a drama production or literary work. All things that happen in the story are either directly or indirectly related to this character.
In "Things Fall Apart", Okonkwo is a warrior and chief of the Umuofia Clan in Nigeria. The story focuses on him, initially mentioning his origins, as the novel tells about his personal story and describes his family. It afterward centers on the experiences he goes through as chief of the Umuofia Clan.
