Diane, I'm holding in my hand a small box of chocolate bunnies...
Diane is FBI Special Agent Dale Cooper's secretary. After being assigned, Cooper addresses nearly all of his tapes to her from that point on, though she has never been seen in the television series or film.
Diane is assigned as Cooper's secretary on his first day working for the FBI, December 19, 1977. He describes her as an "interesting cross between a saint and a cabaret singer," and addresses most of his tapes to her from that moment on, even ones where he appears to be talking to himself.
She appears to show concern for Cooper, as she sends him flowers during his absence after taking a life for the first time.
Diane joins Cooper for a Chinese food dinner on June 10, 1988 and he notes the next day that despite having known her for over 10 years, he does not know her last name.
Special Agent Cooper . . . Dale and I had dinner once. We ate Chinese. We had wonton soup, egg rolls, and Peking duck. That's the one where they inflate the bird with air, swelling it to over double its original size. Without a doubt the most delicious skin I've ever eaten, firm and at the same time delicate. And the meat itself takes on a flavor when slid into the mouth. . . . Well, I couldn't get enough of it.
Behind the scenesEdit
Despite being stated to be Cooper's secretary in The Autobiography of F.B.I. Special Agent Dale Cooper: My Life, My Tapes, some fans theorize that the unseen character does not even exist and is Cooper's way of coping with the loss of Caroline.
Best explanation adheres to the book, that Diane is Cooper's secretary at the FBI. Every time he fills a whole tape he mails it to her and she transcribes it, takes notes, etc. We see him greet her in the office in the movie (FWWM) but even then we don't actually see her. It should also be taken into consideration that when Cooper asks Diane for earplugs, he receives them almost instantly.
The fact that Cooper does receive the earplugs almost instantly, though, is also strange. Cooper mentions the fact that he needs the earplugs on the tape but is never seen phoning Diane to ask her to send them. This would then presume that Diane knows he needs them via the tape. That then means that Cooper has to mail the tape to Diane, Diane has to listen to the tape, then procure the ear plugs, then send them back to Cooper in Twin Peaks. This entire thing took place in a day during the story, which is almost impossible. It is almost as if when Cooper records a message for Diane on the recorder, she gets the information instantaneously and possesses some kind of ability to materialize his needs for him.