Jim, is the straight man. In nearly every successful ensemble comedy, you usually need a straight man to bounce your wackier supporting characters off of.......and that guy usually never gets the credit for the role he's playing.
I loved "The Office", but it really petered out near the end. Probably should have ended 3 or 4 seasons before it did. By the time Steve Carell left the show, they were pretty much toast already.
Had a little bit of a comeback for the final season, but that's only because they knew they were finished by then.