We've talked about several different archetypes of monster here thus far -- the zombie, which includes other mute, lumbering killing machines like Jason and Michael Myers, and the vampire, who if you take away the fangs and the literal need for blood looks a lot like Hannibal Lecter -- but none of these monsters have been too conceptually challenging. (The zombie eats your brain. The vampire drinks your blood. Boom.) By comparison, the Thing Without a Name is downright intellectual.
It's also my favorite. Unfortunately, you don't see the TWaN on celluloid very much, because by its very nature it's difficult to describe, and thus difficult to film. It resides more in the province of horror fiction, where twisted souls like Poe and HP Lovecraft perfected it. Here's the TWaN's deal, in a nutshell: usually an entity from another dimension, another reality or Hell, it's so mind-rapingly horrible that in most cases to even look upon the TWaN means you'll be spending the rest of your days in a straitjacket.
Many of Lovecraft's best stories deal with TWaNs, like his oft-imitated "At the Mountains of Madness," about a team of Antarctic explorers who find the strange ruins of an alien outpost behind a range of long-unscalable mountains. When a few of the the horrible, ululating creatures who live there emerge and chase the team, the one man who looks back at them promptly loses his mind, and is later unable (or unwilling) to describe what he saw. (If this story and its title reminds you of John Carpenter's cruddy In the Mouth of Madness, it should; it's one of many cinematic homages to Lovecraft's work and this story in particular. In it, the latest novel by a Stephen King-esque author named Sutter Cane drives people who read it insane, turning Cane's agent into an axe-wielding maniac and causing riots in the streets. Ooookay.)
Above: in the aforementioned shlockfest, Sam Neill saw something he shouldn't have. Now THAT'S crazy.
More popularly known, Stephen King's It trades on classic Lovecraftian Thing Without a Name tropes. For those of you who only remember Pennywise the Clown, don't forget that "It" was a shape-shifter -- one way to get around never showing your TWaN is to have it manifest itself in different forms "which the human mind can comprehend." Wikipedia elaborates:
"'It' apparently originated in a void containing and surrounding the Universe, a place referred to in the novel as the "Macroverse". Its real name (if indeed It has one) is unknown. Likewise, It's true form is never truly comprehended. Its final form in the physical realm is that of an enormous spider, but even this is only the closest the human mind can get to approximating It's actual physical form. Its natural form exists in a realm beyond the physical, which It calls the 'deadlights.' Coming face to face with the deadlights drives any living being instantly insane."
It's a little corny, maybe, but I really dig the whole it'll-drive-you-insane thing. It trades on larger issues we have as human beings in the world, and -- not to get Biblical on you or anything -- some Old Testament spookiness that I've always found compelling. When Job begs God for an explanation for the horrible suffering he's endured, God finally appears to Job -- but not as a benign old man the sky. Instead Job is confronted by an horrific, baffling whirlwind which some Biblical scholars translate to be called simply "The Unnameable," and the story ends with Job getting no answer and being kind of sorry he asked in the first place; it's made starkly clear that he'll never comprehend the true nature of the universe. Like, wow -- so God is a Thing Without a Name, too!
There are plenty of references to this kind of intense, frightening revelatory experience in religious literature -- what Thoreau calls (paraphrasing) "the light of truth that will put out your eyes." Naked reality is too much for our little minds to handle. It's a theme that's used in religious literature and horror literature alike; two sides of the same coin. Too much knowledge can destroy you -- don't bite the apple; don't fly too high or your wings will melt -- etc etc. My favorite example is the Tower of Babel story: hubristic humans try to built a tower to Heaven so that they might know the mind of God. Instead their tower is destroyed and their minds are confused; the story ends with them running around like chickens with their heads cut off, all speaking different languages. In other words, you don't have to know everything, and in fact it's better if you don't. Look back at Sodom and Gomorrah as God is destroying them and you might turn into a pillar of salt; look back at the horrible Antarctic Elder Being that's ululating behind you and you just might lose your mind.
Stephen King briefly lays out his ideas on the subject (while talking about Lovecraft) in his exegesis on horror, Danse Macabre:
The best of [these stories] make us feel the size of the universe we hang suspended in, and suggest shadowy forces that could destroy us all if they so much as grunted in their sleep. After all, what is the paltry evil of the A-bomb when compared to [Lovecraftian creatures] Nyarlathotep, the Crawling Chaos, or Yog-Sogoth, the Goat with a Thousand Young?"
On the flip side of that coin, at the end of Job, our titular hero also feels the powerful, incomprehensible hugeness of the universe, but rather than losing his mind, he loses his hubris:
"Therefore I will be quiet / Comforted that I am but dust."
In closing, let's rock out to Metallica's take on the subject with their song "The Thing That Should Not Be."