This is a very interesting question, and the answer to it depends a lot on your own personal reading of the poem. My own theory is that the speaker of the poem is both protagonist and antagonist, because it is he who insists on viewing the raven as some kind of supernatural agent of evil, whereas the truth is that it is just a raven and it is the speaker who interprets the response he receives from the raven as being of supernatural import. Note how this is suggested in the following quotation:

`Be that word our sign of parting, bird or fiend!' I shrieked upstarting -
`Get thee back into the tempest and the Night's Plutonian shore!
Leave no black plume as a token of that lie thy soul hath spoken!
Leave my loneliness unbroken! - quit the bust above my door!
Take thy beak from out my heart, and take thy form from off my door!'
Quoth the raven, `Nevermore.'

The reader already knows from the first stanza that the speaker is both exhausted mentally and physically and also that he is grief-stricken. His response to the raven shows that he is his own worst enemy and he is psychologically torturing himself, even though he is not aware of it. It is he who insists on viewing the raven as belonging to "Night's Plutonian shore" and allows the presence of the raven to "break" his loneliness. This is above all a poem that is fascinating because of its psychological exploration of the extent to which a character can torture themselves, albeit unconsciously.