The poem is a first-person narrative, and we experience the events through the eyes of this unnamed man. He is haunted by memories of Lenore and seeks solace in books, but his despair is only amplified by the arrival of a raven, which he mistakenly believes to be a harbinger of hope.
Here's why:
* The poem opens with the speaker in deep sorrow: "Once upon a midnight dreary, while I pondered, weak and weary."
* The speaker clearly misses Lenore: "Ah, distinctly I remember it was in the bleak December, And each separate dying ember wrought its ghost upon the floor."
* The raven's arrival is triggered by thoughts of Lenore: "While I nodded, nearly napping, suddenly there came a tapping, As of some one gently rapping, rapping at my chamber door. "Tis some visitor," I muttered, "tapping at my chamber door Only this and nothing more."
* The raven becomes a symbol of the speaker's despair: "Prophet! said I, 'thing of evil! - prophet still, if bird or devil! - By that heaven that bends above us - by that God we both adore - Tell this soul with sorrow laden, if within the distant Aidenn, It shall clasp a sainted maiden whom the angels name Lenore - Clasp a rare and radiant maiden whom the angels name Lenore."
The raven itself isn't a character with a defined role, but rather a symbolic entity that reflects the speaker's tormented mental state and his inability to find solace in his grief.