The woman in the wallpaper is the narrator. This notion is revealed at the end of the story and it explains the role of women during the time period. The narrator feels like her identity is slipping away and, like the woman, she will fade away into the wallpaper. The entire story builds up to the moment when this idea is revealed. The irony is that those in the story who need to understand, like the husband and sister, do not. The narrator tries to free herself from this dungeon by meticulously peeling off the wallpaper, but her efforts are viewed as madness instead of triumph. Gilman beautifully structures the story so that the reader is privy to all sides; therefore, giving us the great opportunity to pull more from the story than the other characters. It also gives us a slight glimpse into the life of Gilman herself.
The woman behind the wallpaper emerges at the end of the story and is revealed as the narrator herself. Throughout the story, we have seen the narrator descend in to madness exacerbated by her solitary confinement. It is deeply ironic that her husband has fashioned this seeming prison for her based on his medical expertise, and is unconvinced of her mental decline.
If a physician of high standing, and one's own husband, assures friends and relatives that there is really nothing the matter with one but temporary nervous depression--a slight hysterical tendency--what is one to do?
It is her husband whose prostate form she walks over at the end of the story.
"I've got out at last," said I, "in spite of you and Jane. And I've pulled off most of the paper, so you can't put me back!"
Now why should that man have fainted? But he did, and right across my path by the wall, so that I had to creep over him every time!
The woman behind the wallpaper has proved her existence in the mind of the narrator, and has therefore proved the narrator correct in the diagnosis of her own insanity.
The ending of the short story, "The Yellow Wallpaper," suggests that the woman has, in her mind, become the woman in the wallpaper. When she cannot fully remove the wallpaper from the wall and set her free, she becomes her and is thereby set free herself.
The narrator sees herself in an identical position as the woman in the wallpaper, anyway. They are both trapped and imprisoned with no way of escape. The narrator, throughout the story, projects her situation onto the wallpaper print, and becomes obsessed with setting the woman she perceives in the wallpaper free.
When she cannot, she becomes her. In her words:
I wonder if they [women outside of her room] all came out of that wallpaper as I did?
I suppose I shall have to get back behind the pattern when it comes night, and that is hard!
Having begun the narration with what we today call post-partum depression, the woman closes her story completely identifying herself with the woman in the wallpaper.