Antagonist
Character Role Analysis
Antagonist: Hill House / Eleanor / Eleanor's Mother
Who's the antagonist of the novel? We really can't say. Not because the novel doesn't have an antagonist—it definitely does—but because the antagonist's identity remains cryptic throughout the story. Discovering the antagonist's identity will depend on your reading of the novel and how you decipher its various clues.
If you feel there's a good case to make for Hill House being haunted, then you could say the setting itself is the antagonist. But you could just as easily make a case for Eleanor's own self-absorbed psyche. In this case, Eleanor would be hero and villain at the same time. Then again, perhaps the ghost of Eleanor's domineering mother is the true culprit as well, or the guilt Eleanor feels for letting her mother die. We suppose you could even make an argument for Hugh Crain or Theodora being the antagonist, although these possibilities didn't leap readily to our minds.
The point is that Eleanor gets into a conflict with something at Hill House over her sanity. But no one—not even Eleanor—can say with certainty what that something is.