The narrator’s real battle in the story isn’t with another character, but with whatever it is that haunts the room. It’s fear that haunts the room, and fear that the narrator has to fight within himself. He also combats it physically, since the darkness of the room is both the cause and the symbol of his fear (see "Symbols, Imagery, Allegory" for more). It’s against fear that the narrator and his reason lose their battle. (Recall that he tries to ward off the darkness with his candles.) It is ultimately Fear, which almost kills him (well, fear plus whatever it is he runs into). Fear is then presented at the story’s end as the universal enemy of human reason and of human beings themselves.