Who is the antagonist in On Writing: A Memoir of the Craft by Stephen King?

On Writing: A Memoir of the Craft is a nonfction book, and as such, does not include an antagonist. Stephen King does, however, discuss the various types of characters used in fiction. As an example, Stephen King discusses Annie Wilkes. Annie Wilkes is the antagonist of his novel, Misery. Annie is a psychotic nurse who takes her favorite author hostage in order to force him to write a novel that brings the main character back to life. Annie is insane. There is no question of this when the quiet, mild mannered woman suddenly cuts off her captor's foot when he tries to escape. However, Stephen King finds sympathy with this woman through the development of the novel, and this comes across in his writing. It is for this reason that Stephen King uses her as an example as he wants the reader to see that all characters are multi-dimensional rather than like cardboard cutouts.