The Darkhold Dwarf is a demonic villain originating from Marvel comics, though the work he comes from is notable for being more openly horror-themed and thus dealing with more graphic, disturbing content than most of the superhero stories that Marvel is more famous for producing.
He is a monster whose very existence is tied to the elder-god Chthon and his cursed Darkhold, which played a major part of the series and was the central force of evil within its setting, in many ways the Darkhold Dwarf can be seen as a living embodiment of the Darkhold and sought to bring the cursed powers of the text into reality via appearing to evil minded people or foolish victims, presenting them with a page from the Darkhold so as to inevitably cause chaos and misery via the dark magic they would unleash.
The Darkhold Dwarf is immortal and unable to truly be defeated short of destroying every copy of the Darkhold, as he will continue to manifest wherever a page of the tome exists, he is highly devious and possesses near-omniscience, though this is somewhat limited both by his evil nature and his obsession with spreading the Darkhold's influence across reality.
For all his power and dread he is still significantly below the ranks of an elder-god such as Chthon, who created the Darkhold and many other dark magic relics, as well as the being of true chaos to which the Darkhold Dwarf serves.