"[Leatherface] is never an object of pity per se, but is clearly not your standard masked maniac who delights in the torments of his victims. He is the very banality of our primal basic animal nature; no motive, no ambitions, no conscience and no soul. It exists merely to survive and provide for itself and its family."-- "The Texas Chainsaw Massacre," essay by Michael Feischer, HORRORHOUND magazine, Jan/Feb 2013.Though I don't quite get why essayist Feischer changes pronouns in midstream from "he" to "it," the fact that he does so might demonstrate that the concept of the monster is one that makes it hard to distinguish between sentient life and non-sentient objects. A few of the monster-movies I've reviewed on NATURALISTIC! UNCANNY! MARVELOUS! even include "monsters" who are nothing more than non-sentient phenomena gone berserk, though it's more often that they're giant versions of creatures found in nature-- spiders, birds, octopi, etc.
Feischer (presumably no relation to the similarly named comics-writer Michael FLEISCHER) is only talking about one monstrous figure, but I would say that parts of his description work for my concept of the monster-persona, particularly the reference to "basic animal nature" and the focus upon survival of itself and its ingroup.
I certainly would not typify monsters as being without "motive," "ambitions," "conscience," or "soul," however. A mad scientist like Wells' Doctor Moreau, examined here, has both motives and ambitions, although he has no conscience and arguably no soul. In contrast, many monsters are appealing precisely because they are aware of their monstrous nature and struggle to some extent against it, even if they fail to triumph, as I recently observed in the case of the two BLACULA films.
Perhaps one appeal of the monster is that he has an "animal nature"-- which for me is the same as an "instinctive will"-- that he often fights against, though often unsuccessfully. The rare monsters that manage to succeed are those that, like the Hulk and the Swamp Thing, do manage to become serious heroic protagonists. Comic monsters like Dick Briefer's Frankenstein must be considered successes of a sort, though since they occupy a comic universe, their struggles are by their nature lacking in deep conviction.
On another matter, I wrote in the above-cited essay:
The difference in the degree of negativity, however, makes me label Wells' Doctor Moreau a "monster" rather than a "demihero."
This doesn't contradict anything I've written, but I want to clarify that though the demihero does have some potential as a vessel for negative, life-denying forces-- and can even transform rather easily into the figure of the monster-- on the whole the "instinctive will" governing the demihero is the positive mirror-image of the "animal nature" Feischer references. At times demiheroes are set up to be unequivocal victims, whether they are sympathetic or not, but they have a quality of "persistence" equal to that of the monster, and so are capable of turning the tables on their monstrous doubles-- though usually with the sort of "glorious" attitude of the hero triumphing over the villain.