Antagonist
Character Role Analysis
The Social Hierarchy
We know that you want to put the blame on the prominent personage, but his mean disposition is not exactly his fault. He's a good guy at heart, but the social hierarchy makes him act all strange and horrible.
The antagonist is the thing that keeps the protagonist from getting what he wants. If most people didn't think that Akaky was at the bottom of the ladder, someone might have helped him find his coat, but because of his low rank, people either don't pay attention to him, are suspicious of him, or are deliberately mean to him. Akaky wants his coat, but the rules and regulations of Russia's social hierarchy are the reason that he has to come back from the gate grave to get it.