True, the narrator can be all of those things. Some examples include the following:
Major Character who's the narrator: Hazel Grace Lancaster in The Fault in Our Stars
Minor Character who's the narrator: Nick Carraway in The Great Gatsby
Protagonist: Esther in Sylvia Plath's The Bell Jar (narrated in 1st Person POV)
Antagonist: Amy Dunne in Gone Girl by Gillian Flynn
