* Harold Crick: A mild-mannered IRS auditor, played by Will Ferrell. He's the protagonist and the subject of the narrator's story.
* Kay Eiffel: A baker, played by Maggie Gyllenhaal. She's Harold's love interest and a catalyst in his journey.
* Anna Pascal: A literary scholar, played by Emma Thompson. She's the author of the fictional story Harold is living in.
* Jules Hilbert: A professor of philosophy, played by Dustin Hoffman. He's Harold's mentor and provides philosophical guidance.
* Dave: A fellow IRS auditor, played by Queen Latifah. She's Harold's friend and confidante.
* Narrator: A voice-over, whose identity is initially unknown but later revealed to be a fictional character within Anna's story.
There are other supporting characters in the film, but these are the major ones who drive the plot.