The Host of Suffering is a death knight order under the command of the Lich King. It succeeded the death knights of Acherus who were, for the most part, freed of the Lich King's will after the Battle for Light's Hope Chapel.
They are based in Malykriss: The Vile Hold, a Scourge necropolis under construction in Icecrown. Once completed, their necropolis will be all but indestructible.
As one of the last powerful remaining Death knights of Acherus, Orbaz Bloodbane was appointed as the commander of the order, receiving the title <The Hand of Suffering>.
Like in Acherus: The Ebon Hold before, there are three different death knight masters, each one teaching the adepts a path of the abilities of a death knight.