The narrator of Camus' The Plague is Dr. Rieux. Although he states this directly only at the end of the novel, there are some hints that foreshadow the final revelation. In the exposition developed by Rieux as the unnamed first-person narrator, he does two interesting things to foreshadow his disclosure while setting up the narratorial point of view.
One is that he promises to reveal the identity of the narrator in "due course": "the narrator (whose identity will be made known in due course) would have little claim to competence for a task like this, had not chance ... closely involved [him] in all that he proposes to narrate."
The other is that he, as the narrator, includes himself in the community of Oran; he's not an outsider. He does this by using first and second person plural (e.g., we, us) and possessive and reflexive pronouns (e.g., our, yourself).
The foreshadowing techniques allow Rieux to develop himself as a narrator who is there, who is personally involved in events, having first-hand knowledge of them, before he discloses his identity. His commitment to facts and truth also casts him as an objective narrator with "justification for playing the part of a historian."
The language he used was that of a man who ... had resolved ... to have no truck with injustice and compromises with the truth.
At the end of The Plague, Rieux reveals himself to be the narrator of the novel. Unlike a typical first-person narrator, Rieux refers to both himself and others in third person. This technique allows him to give a more objective account, as if he is offering a testimonial on the crisis rather than merely expressing his personal feelings or drawing assumptions about others' reactions and motives. To present a balanced portrayal of the events that occur during the plague, Rieux also refers to details that another character, Tarou, records in his diary.