The host of The Colbert Report is reporting for comedic duty on The Office! Stephen Colbert will guest-star this season as Broccoli Rob, a former member of Here Comes Treble, Andy’s a cappella group, EW has learned. In the Halloween-themed episode, Andy (Ed Helms) discovers that the smarmy, competitive Broccoli Rob is singing a different tune about the history of the group and stirring up drama, which only intensifies the rivalry between these two frenemies.