Seer Rhee is Sonmi's boss, for lack of a better word. By boss, we mean "shift leader at McDonald's," since that's pretty much what Papa Song's is—the McDonald's of the future, complete with Golden Arches.
Even though he's in charge, it's really just a semblance of power. He's a victim of corpocracy just as much as Sonmi is. "Like many of this dying corpocracy's purebloods, he clung to the belief that hard work and a blemishless record were enough to achieve status" (5.1.38). He never achieves anything, though, and commits suicide for an unknown reason. Maybe it's because he works his butt off in a soulless job and stays stuck in the same social class and tax bracket. Yoona-939 says, "He has lived with fabricants for so long he is very nearly one of us" (5.1.46). He, too, is devoured by corpocracy.