Stranger Than Fiction

Harold Crick, an agent for the Internal Revenue Service, lives his life by his wristwatch. He is assigned to audit an intentionally tax-delinquent baker, Ana Pascal, to whom he is attracted. On the same day, he begins hearing the voice of a woman omnisciently narrating his life but is unable to communicate with it. Harold's watch stops working and he resets it using the time given by a bystander; the voice narrates, "little did he know that this simple, seemingly innocuous act would result in his imminent death". Worried by this prediction, Harold consults a psychiatrist who attributes the voice to schizophrenia, though they consider that if there really is a narrator, he should visit an expert in literature. Crick visits Jules Hilbert, a literature professor, and relates his story. When Jules recognizes aspects of a literary work in Harold's story, he encourages Harold to identify the author, first by determining if the work is a comedy or tragedy.
As Harold audits Ana, the two fall for each other, but when Harold refuses to accept cookies that Ana made for him because they could be viewed as a bribe, Ana tells him to leave, making Harold believe the story is a tragedy. On the advice of Jules, Harold spends the next day at home trying to control his destiny by doing nothing, but his apartment is partially demolished by a wrecking crew that mistook the building for an abandoned one. Jules believes that since Harold cannot control the plot, he should accept his impending death and enjoy whatever time he has left. Harold takes a vacation from work, develops his friendship with his co-worker Dave, fulfills his dream of learning to play the guitar, and dates Ana. Harold reassesses his story as a comedy. When he returns to Jules with this revelation, Harold inadvertently identifies the voice in his head from a television interview as author Karen Eiffel. Jules, an admirer of Karen's work, reveals that all of her books feature the main character's tragic death.
Karen struggles from writer's block and researches ways to kill the character Harold to complete her next book. Her publisher sends an assistant, Penny Escher, to ensure the book is completed. Harold finds Karen through her tax records. When Karen learns that Harold experiences everything she writes, she is horrified by the thought that her books may have killed real people. She tells Harold she wrote a draft of his death, but has not typed it up yet; the events in the book manifest when she strikes the period key. Penny suggests Harold read the drafted ending to get his opinion. Harold cannot bring himself to read it and gives the manuscript to Jules to review. Jules confirms its excellence, labeling it as Karen's masterpiece; Harold's death is integral to its genius. Though Harold is distressed over his fate, Jules comforts him by stating the inevitability of death: this one death, at least, will have a deeper meaning. Harold reads the manuscript, then returns it to Karen, telling her the death she has written for him is "beautiful" and she should keep it intact. He spends one last night with Ana.
The next day, Harold prepares to return to work, despite Karen's voice narrating as she types up her ending. Because Harold's watch is three minutes fast owing to the imprecise time given to him days ago, he reaches the bus stop early and watches as a young boy falls in front of the oncoming bus. Karen continues writing; Harold leaps from the curb and pushes the child out of the way, but is struck by the bus. Karen cannot complete the sentence confirming Harold's death, and Harold wakes up in a hospital, injured but alive. He learns that fragments of his wristwatch blocked the right ulnar artery in his body after the collision, saving his life. When Jules reads Karen's final manuscript, he notes that the story is weaker without Harold's death. Karen admits the flaw, but points out that the story was meant to be about a man that dies unexpectedly; with Harold sacrificing himself, the story would have lost its tragic impact. In place of Harold, his wristwatchâanthropomorphized throughout the filmâis the character who died tragically.

Question: Who's voice is in Harold's head?
Answer: author Karen Eiffel