The high priests, @, are the head of all religious activities related to the deities. There are exactly four in the game: three corresponding to each of the deities of the player's pantheon (who appear in the High Temples on the Astral Plane) and the high priest of Moloch (who appears in Moloch's Sanctum). Additional high priests may appear if an aligned priest gains experience. As with aligned priests, they are generated with a mace, small shield, and one of a robe, cloak of protection, or cloak of magic resistance.
The high priest of Moloch holds the Amulet of Yendor, and it is extremely likely that killing him will be necessary to obtain the Amulet. This can be difficult, and players will tend to save a wand of death charge for the specific purpose of killing him; this will not work if he is generated with a cloak of magic resistance. He turns hostile once you step into the room holding the High Altar of Moloch, so be prepared before opening the door. Note that killing him before stepping in the temple (and subsequently turning him hostile) counts as murder for lawful and neutral characters.
The high priests on the Astral Plane are always generated peaceful, and will remain that way unless you provoke them.