From PathfinderWiki

Among the countless legions of daemons on the plane of Abaddon, a few are able to distinguish themselves and rise in power above even the deacons of the Horsemen of the Apocalypse. These unique individuals are collectively known as harbingers, and they rank in power above all other daemons, save the archdaemons. Most maintain small cults on Abaddon and elsewhere, granting power to their worshipers. They are largely subservient to one of the archdaemons, although they are also their greatest competitors.1

Known Harbingers

The true number of daemonic harbingers is said to be in the hundreds. Below is a short list of the best known members of their evil fraternity.1