Who is the antagonist in "Bartleby the Scrivener"?

The true antagonist in this story, according to the lawyer who narrates it, is not Bartleby, but the hopelessness that arises from failed communication. At the end of the saga, the lawyer reveals a rumor he has heard that Bartleby was previously employed in the dead letter office in Washington D.C, where letters that never arrived at their destinations are sent to be burned. This gives the lawyer a flash of insight into Bartleby's melancholy nature:

Dead letters! does it not sound like dead men? Conceive a man by nature and misfortune prone to a pallid hopelessness, can any business seem more fitted to heighten it than that of continually handling these dead letters, and assorting them for the flames?

This ending sheds light on to Bartleby's seemingly inexplicable desire to prefer not to do any work at all. If all effort is futile, if all words are doomed to perish unread, why would a scrivener—a copier of words—continue to make an effort?

The lawyer is a rare sensitive soul who shows compassion for Bartleby and tries to understand him, even if, in the end, he can not keep him in his employ.

Who is the antagonist in "Bartleby the Scrivener"?

Bartleby is the antagonist to the old lawyer, the protagonist who tells the tale. At first, Bartleby is a hardworking, conscientious employee, almost a model worker. But after a while he just stops working. In fact, he stops doing anything. In most cases, the antagonist is a character who actively does something to antagonize others, but that's not the case here. Bartleby is an antagonist without doing anything at all. And his passivity and inertia make him a particularly effective antagonist because it's very difficult to counter inaction with action. In telling his story, the lawyer admits that he's met some strange individuals in his time but none like Bartleby. He is so mysterious, so utterly inscrutable, that it's virtually impossible to deal with him. In the end, only drastic measures will do, and even then Bartleby remains every bit as much of an antagonist in the confines of a prison cell as he was in the office.

Who is the protagonist of "Bartleby the Scrivener"--Bartleby or the lawyer/narrator?

With the apparent propensity of Herman Melville for writing narratives in which characters have doubles--in Moby Dick, Ahab has two alter egos:  Pip as his imaginative side, and Fedulla as his darker side--there is a substantial argument for Bartleby's being a double for the lawyer.  Thus, as the lawyer's "psychological double" that represents the impersonal and sterile side of him, Bartleby acts with him as both protagonist and antagonist. 

In his essay, "Melville's Bartleby As Psychological Double," Modecai Marcus proposes that the screen which the lawyer places between himself and Bartleby represents his attempt to subjugate his imagination and sensitivities to the world of business.  For, Bartleby works industriously for the religiously significant three days, then stops producing; instead, when asked perform tasks, Bartleby simply replies, "I prefer not."  While the lawyer is at first the antagonist, Bartleby's passive protests increasingly dominate the lawyer, making him now the antagonist.  As Marcus points out,

The lawyer finally accepts Bartleby's presence as a natural part of his world, and he admits that without outside interference, their strange relationship might have continued indefinitely.

However, the roles of protagonist/antagonist reverse as with the increasing resistance of Turkey and the other scriveners, the lawyer feels compelled to dismiss Bartleby. Still, after he learns that Bartleby is living in his office from which he has moved, he invites Bartleby to come home with him until he can find lodgings.  But, then, Bartleby becomes again the antagonist, refusing the lawyer's offer.  Finally, when the lawyer learns that Bartleby has been taken to prison and blames him for this imprisonment.  Marcus suggests that Bartleby, who stares vacantly at the prison wall, represents a "voice deep within the lawyer" that wishes to give up his way of life on the confining world of unimaginative business on Wall Street. Therefore, Bartleby resumes the role of protagonist.

Thus, in Herman Melville's story, "Bartleby, the Scrivener, A Tale of Wall Street," Bartleby and the lawyer represent conflicting sides of the mind of one individual who has been reshaped by the limitations of society, symbolized as the "wall."  Like Ahab, who refuses to accept his limitations as a damaged man and seeks to break through "the pasteboard mask," the lawyer, too, struggles as his does hi psychological double, Bartleby;  they struggle to combat the "wall" of limited imagination. 

Who is the central character in "Bartleby, the Scrivener," the narrator or Bartleby, and why?

Given that the action of Melville's existential fable is seen through the narrator's eyes, one can argue that he is the central character: the story is told from his point of view, not Bartleby's. Bartleby himself is less a "character" in the realistic sense than a symbol, an emblem of that segment of humanity, or of the human tendency, that reacts negatively to what it perceives as a meaningless universe. Bartleby steadily withdraws from the world, seeing no reason to act as people normally do. He retreats into a mode of complete passivity. All of this is described as the narrator witnesses it, and it is his bafflement at Bartleby's actions (or lack of them) that constitutes the emotional and rational content of the tale.

That said, it is Bartleby's own negative and withdrawn mindset that projects to us the "message" of the story. Therefore one could also argue in favor of his centrality to the story, more from a philosophical than from a narrative standpoint. Bartleby is similar to Hawthorne's Parson Hooper in "The Minister's Black Veil." Both are men who are prototypes of the dark side of humanity—not dark in a criminal sense, but in the guise of hopelessness and indifference to the active life that most of us find worth living.

Who is the central character in "Bartleby, the Scrivener," the narrator or Bartleby, and why?

Both. Bartleby is the central character, but we view his actions through the perspective of the narrator. That being said, in the absence of a first person narrator, the reader would certainly consider Bartleby as the central figure. The narrator's reactions to Bartleby's serve to heighten Bartleby's seemingly bizarre behavior: his almost nihilistic or absurdist "passive resistance."  The lawyer (narrator) eventually becomes fascinated by Bartleby, further underscoring the idea that Bartleby is the main character.

Think of the movie "Office Space," if you've seen it. Peter is the main character: the Bartleby who "prefers not to do his work." A more comedic, less dark version to be sure. But still, while Peter is the main character, we relate to him and his dissatisfaction with his boring, working class life. But we also look to the other characters for their reactions to Peter's behavior in much the same way we look to the lawyer's (narrator's) perspective and interpretations of Bartleby's disenchantment.