This is a named mob in the Plane of War. For an overview of all nameds in the Plane of War, their PHs, map points, and mapped locations, see this quest entry.
"Rolfron Zek, Lord of Despair" (click for map image) spawns in the northern part of the Mines (PH is "Dejected Kobold" with respawn timer of 10-12 minutes).
Rolfron Zek hits for a max ~29,000 (no rampage; no flurry).
He has three "Anguish of the _____" debuffs, cast on seemingly random targets, three at a time (including pets of all types). None of these "Anguish" spells should be cured, as they have detrimental effects for doing so (curing "Anguish of the Body" results in "Crushing Anguish" while curing "Anguish of the Soul" and "Anguish of the Spirit" results in the curer being silenced from casting further cures for a bit).
He also has three "Despair of the _____" random-target spells (again, three at a time, including pets of all types). "Despair of the Body" is a lifetap while "Dispair of the Soul" and "Despair of the Spirit" do up to 90,000 dmg (damage amount is calculated based on how many hitpoints, mana, or endurance the target has). These may also drain endurance and mana.
Rolfron also spawns adds ("a shadow of despair") in waves of 2-5 at a time (either the longer he's up OR the lower in health he gets, the more adds per wave). These hit for a max ~16,000 and have relatively few hitpoints. They "die" on their own after a short time of being up. It's unclear if they have to be killed to avoid punishment mechanics, or if they can be left alone. Nothing appears to happen when an add is killed, or when an add dies on its own.
A death touch called "Annihilation of Despair" may also occur here, but the trigger for it is not known.
Rolfron Zek, Lord of Despair says 'Suffer as we have suffered!'
Rolfron Zek, Lord of Despair has been slain by _____!
Spirits of sorrow quickly escape the fallen god's husk. Despair will soon reign anew.