Is the antagonist the double, or the narrator himself? Possibly those are the same thing, which should make sense to you if you read the epigraph or any of Shmoop’s analysis. William dogs himself around the world, makes himself miserable, even kills himself, or rather, a part of himself by the story’s end. He is his own worst enemy. Another interpretation is that the second William Wilson really is a second person, who just happens, purely by coincidence, to look exactly like the first William Wilson and obsess over making him behave.