The narrator is most clearly a monster due to the fact he enjoys being mean for fun (letter A). "Notes from the Underground" is a novella throughout which Fiodor Dostoyevsky, one of the most respected Russian authors of all time, who lived and died in the 19th century, explores the narrator's flaws, weaknesses and limitations to the fullest, and the most bewildering thing about it is that the narrator himself is who outlines all of it mercilessly. Dostoyevsky, who also wrote "Crime and Punishment" and "The Brothers Karamazov", among other works of deep human analysis, truly mastered the art of characterization, and his characters were all full of issues, especially due to their difficulty in fitting in, in accepting a world where capitalism and a hierarchical society dictate all values and establish who's supposed to be prosper and who's supposed to obey and be miserable. This is no different in "Notes from the Underground", where the narrator shows us how offended he is by the people who treat him with condescension. Maybe he's a monster, but one who developed such a trait due to his restless, uneasy mind which is deeply affected by the people around him.
