The person knocking on the narrator's door that night was the raven, who kept saying, "Nevermore."
What were the events that happened on the night of the knocking on the narrator's door?
Someone knocked on the door, startling the narrator. There was nobody there when he opened the door. He turned to face the space. After shutting the door, he returned to his room.
When there was a knock on the door again, he opened it to see a raven perched on the ledge. The raven entered the space and settled itself on Pallas's bust. Upon being asked its name by the narrator, the raven said, "Nevermore."
The raven then answers the narrator's question about seeing his deceased love again with the words "Nevermore."
In desperation, the narrator shouted, “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!”.
In response, the raven said, "Nevermore." At that point, the narrator understands that the raven represents his sorrow and hopelessness and that he will always be affected by them.