"Don't you understand? Before Joe Gillis came along, Norma Desmond was fucking the monkey!"
At Andrew Lloyd Webber’s opening night party for his musical version of Sunset Boulevard (1950), Billy Wilder provided that answer to a woman asking about the role of the mysterious dead chimpanzee introduced early in the film.
Wilder used to tell Gloria Swanson that her character, Norma Desmond, was in a sexual relationship with the chimpanzee. He reminded her of it repeatedly, but being a known jokester, she took his claims at face value. That is, until one day he reportedly directed her by using the word, saying, “One more time, Gloria, and show us what you feel. Remember, Norma Desmond was fucking the monkey!”
Wilder never provided any concrete answer on whether or not this was really his design for the chimp. While it is noted by her butler and first ex-husband Max (Erich von Stroheim) that Norma has been “married” three times, we never learn what became of the husbands between Max and the present. Maybe the chimp was one of them. Or, less crazily, perhaps the chimp is nothing more than a reflection of the lavish and unusual commodities of an eccentric celebrity, and in the context of the film, a symbol for the life Joe Gillis (William Holden) would come to lead within the walls of Norma’s cold mansion.
When Joe pulls into Norma’s garage, she and Max immediately mistake him for a mortician bringing a coffin for the chimp. Not knowing Norma, Joe doesn’t inquire deeply as to why she has a dead chimpanzee with whom she seems so attached. But she is a unique and rich old movie star, so having a pet chimp wouldn’t be a terrible surprise.
Of course, a chimp is also an animal that can be trained and controlled, pantomiming human behavior without the intricacies of human speech or nuance. Much in that same way, a silent film star would go about their craft. The chimp serves as a symbol of the dead era from which Norma came, where actors were trained to behave in certain exaggerated human-like ways, but couldn't transition beyond that behavior.
Similarly, Joe ends up trained by Norma. She provides him with the necessities of life as well as extended pleasures, and in turn he does whatever she asks of him. Though he was failing and broke before coming to her house, he lived in a world of reality. After Norma took care of his debts and adopts him into her lifestyle, he becomes like a trained animal. She needs to know who he talks to and where he goes. He works on her script the way she wants, though he is the writer. And like the chimp, his experiences with Norma end with him dead in her back yard. The shot of the dead chimp is a companion shot to the one of dead Joe as he assumes its role by the end of the film.
The night of the chimp’s funeral, Joe has an odd vision. He tells us, “That night, I had a mixed-up dream. In it there was an organ grinder. I couldn't see his face, but the organ was all draped in black, and a chimp was dancing for pennies. When I opened my eyes, the music was still there...Where was I? Oh yes, in that empty room over her garage.”
When he wakes up, all his belongings have been brought to Norma’s house. At that point, he becomes hers. He becomes her new chimp.