The Cleaner

The Cleaner is a black level 63 elite demon. Although he looks like a black dreadlord he appears not to be one.

Abilities
He could hit for 4500-5000 on a lvl 70 cloth wearer and was said to be immune to all damage.

Source
The Cleaner spawned when someone besides the hunter attacked Simone the Seductress during the level 60 hunter quest Stave of the Ancients, and proceeded to kill the interloper and the hunter while Simone despawned. He could also be triggered by attacking Simone in her troll form, however you needed to have over one player or mob on her aggro table, otherwise she would simply kill you with her Fool's Plight.

He also spawned if someone interfered with a priest doing the The Balance of Light and Shadow (quest) quest.

It seems that a Cleaner spawned whenever damage was dealt by an outsider source, therefore more than one Cleaner could be spawned at the same time.

Quotes
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