The main characters are Mort Rainey, a writer, and John Shooter, the man who accuses Mort of plagiarism.
There are two main characters in 'secret window short story'. One is Mort Rainey. He's a writer who is having a hard time in his life, especially after his wife leaves him. The other is John Shooter. He's the mysterious figure who shows up at Mort's place and claims that Mort has stolen his story. Their interactions form the core of the story.