Fahrenheit 451 is written from the limited third-person voice of Guy Montag. In this story, the narrator [the persona the author takes within the story] is the main character. Thus, to answer the question of how the narrator views the main character, we have to ask how the main character views and perceives himself.
In the beginning, Guy Montag doesn't engage in much self-reflecting. He's busy burning books, with pleasure. Guy's interior mental world is not very rich, so his thoughts about himself don't have much depth. For example, when his wife asks if he is happy with his job, Montag initially responds with a nearly automated internal "yes." It is a "yes" that bubbles to the surface of his mind without any critical self-reflection on Montag's part. Outside of his identity as a fireman, Montag doesn't have any sense of who else he might be. His sense of himself as a person is one-dimensional and limited in scope.
As the story progresses, Montag develops more open and complex ideas about himself. He entertains doubt concerning right and wrong; he begins to exercise agency; and, he begins to effect change in the world around him. By the end of the story, Montag sees himself as a fully developed, autonomous person -- one who can act in the world in order to make the world a better place.
This radical transformation in self-perception does not occur at any particular moment in the story, but instead occurs bit by bit as Montag interacts people who challenge his perceptions, and as he takes greater and greater risk in pursuit of personal freedom.