Dusk is a powerful demonic being from Marvel comics and is related to Nightmare - like Nightmare Dusk is also an embodiment of a negative abstract concept - namely madness in all it's forms: he rules a dimension so troubled that even Nightmare fears it, known to mortals as the Realm Of Madness.

Within this Realm, Dusk commands innumerable lesser-demons of madness, who embody specific conditions such as Delusion, Dementia, Fetish, Megalomania, Necromancer, Neurotica, Obsession, Paranoia, Phobia, Psychosis and countless others - Dusk is the most powerful of them all and is basically the sum total of all insanity in the Marvel universe.

It is stated that all who go mad will eventually gaze upon Dusk and he has the frightening power of being able to transform himself into anything the insane can think of (granting him almost unlimited potential).