The jacket that Paul Giamatti wears for Harvey's first "Late Night with David Letterman" (1982) appearance is the exact same piece of clothing that we see the real Harvey wearing on the TV.
Jonathan Demme had tried to adapt a film version of "American Splendor" in the 1980s, but the project never came to fruition as Demme wasn't an established director.
'Rob Schneider' and Leonardo DiCaprio was considered for an early film version of the book.
All of the "white room" documentary scenes were filmed in one day.
Cameo: [Gary Dumm] longtime American Splendor artist is the gray-haired man getting his copy of "Our Cancer Year" autographed.
Harvey says that there has already been a film made about Robert Crumb. This is, of course, Crumb (1994).
NBC would not lease out the actual "Late Night with David Letterman" (1982) footage where Pekar finally lashed out at Letterman, so the scene had to be recreated with the actors.