Hulu's Castle Rock season 2 featured Stephen King's iconic character Annie Wilkes from his 1987 novel Misery, but the showrunners made several major changes from the original book character in order to fit her into the series' storyline. Castle Rock takes place in Castle Rock, Maine, one of the three well-established fictional towns created by the horror author. Several of King's short stories, novellas, and novels take place in Castle Rock, but Annie Wilkes' story does not, so why did they choose to make her the villain and how were they able to accomplish this feat?
Annie's original story takes place in Colorado and begins at a book signing with her favorite author, Paul Sheldon. The 1987 novel is based on the relationship between fans and the celebrities they idolize to the point of delusion. After she attends the event, the author gets into a car accident and wakes up to discover that Annie has taken him captive in a remote cabin, where she forces him to rewrite his latest installment in the Misery book series. In Castle Rock, Annie begins her story as a single mother traveling with her daughter, Joy, for seemingly no real reason. After getting stuck in Castle Rock, Maine, Annie takes an RN position and steals prescription medication. As season 2 progresses, she becomes increasingly unhinged to the point where, when her daughter dies, she believes her to still be alive and hallucinates her existence.
Castle Rock features several characters from Stephen King's novel as well as numerous notable alumnae from his movies such as Sissy Spacek from Carrie as well as Bill Skarsgård from Andy Muschietti's IT: Chapter One and IT: Chapter Two. While Castle Rock season 1 focused on the events surrounding The Kid (Skarsgård) and the Shawshank State Penitentiary, season 2 focused on the origin story of Annie Wilkes, portrayed by Lizzy Caplan. Her origin story did not exist prior to the Hulu series — here's why it likely had to change.
In Misery, the only known background about Annie Wilkes is her occupation as a nurse and the fact that she adores the works of Paul Sheldon. Castle Rock made a major change from the book by giving her a daughter as well as an origin story. While she has always been relatively unhinged, her true delusion does not begin until she loses her daughter by the end of season 2. As it concludes, Annie is seen waiting in line at a book signing for her favorite author, Paul Sheldon, while hallucinating that her daughter is there with her. By creating this origin story, the showrunners establish that her unstable nature in Misery was a byproduct of the trauma she experienced from killing her daughter that converged with her already faltering mental state.
While this major book change was made in order to establish her origin story and create a strong background context to the 1987 novel, it also worked to make her the villain of Castle Rock season 2. In the source material, Annie has never lived in Maine nor does she ever allude to traveling across the country with a daughter. As far as readers are concerned, Annie Wilkes was born and raised in Colorado. While season 1 was full of characters from stories set in Castle Rock, season 2 does not include any. The only original Stephen King character is Annie Wilkes. The reason that the showrunners likely made her the villain is due to the fact that there are not many villainous characters that exist in the Castle Rock literary canon.
With the few characters it had to go off of, the showrunners most likely chose Annie Wilkes because of her iconic status as one of the most unsettling villains of King's creation as well as her lack of backstory — they could create their own. Including a character without that backstory provided the opportunity to include their own original content that would, in turn, better Castle Rock season 2's storyline in the absence of other choices for a lead villain.