Harvey Pekar is a comic book writer in reality and fiction. The real Pekar narrates this film, as well as being included in scenes interpolated with the narrative. Paul Giamatti plays Pekar in the narrative. Additionally, there's the comic book dimension, which takes us further into the fictional Harvey Pekar. See, Pekar writes comics about himself; he's egocentric that way. Pekar provides us with a glimpse of his aged, calmed self. Contrastingly, Giamatti gives us a younger, sloven mope. The comics give us varied pictures--it depends who the cartoonist is.
Pekar, as played by Giamatti, is a lackluster protagonist; he's an obsessive-compulsive neurotic who whines about the virtues of the everyman. He's repulsive--his home is a mess and he scratches his head incessantly. He should try new shampoo and conditioner, or perhaps he doesn't wash very often.
I guess the point is Pekar's genius rests in his presentation of ordinary life, or at least the ordinary dork's life. While this doesn't seem a bad idea for comics, I don't read comic books. Robert Crumb was one cartoonist of Pekar's, I gather, underground cultist "American Splendor" series. Watching James Urbaniak's personification of Crumb, I felt the urge to watch the documentary 'Crumb,' again; the medium used there made it seem... well, more real.