Dave Lebling introduced a similar monster, whose name was borrowed from Vance's grues, into the interactive fiction computer game Zork. Zork's grues fear light and are ravenous devourers of adventurers, making it impossible to explore the game's dark areas without a light source.
Further investigation will reveal more about their nature:
This warning is not to be taken lightly. If the player attempts to continue moving through a dark place rather than returning to a lit area or activating a light source, there is a high probability he will be caught and eaten by a grue. Originally, grues were not a threat as long as one remained still and didn't leave one's location, but in later games it has been possible, in certain situations, to be eaten by a grue simply by waiting around in the dark.
Grues were invented to limit players' options when faced with unlit areas. If a player should attempt to blunder about in the darkness in hopes of achieving whatever goal first brought them there, the presence of grues ensures that they will fail, forcing the player to solve any light-related puzzles first. Zork's predecessor, Colossal Cave Adventure, used bottomless pits to achieve the same result, but when early versions of Zork adopted this practice, it was realized that pits were appearing in unlikely places, such as the attic of a house, and with no corroborating evidence elsewhere (such as holes in the ceiling—or floor!—in the room directly below). Thus, Dave Lebling envisioned a wandering, light-fearing monster that could do the job of the bottomless pits, and, taking the name from Vance's work as having the right connotations, introduced grues in the next version of Zork. The version update document made a humorous reference to the "dungeon maintainers" painstakingly filling up the bottomless pits and restocking the dungeon with grues. Years later, the Zork prequel game, Zork Zero, would feature the protagonist doing exactly that: forced to use a magic device to seal up the realm's bottomless pits that are blocking his path, he unwittingly forces out the myriad colonies of grues that have been nesting there, leaving them to wander the underground caverns searching for food.
Much is made of the idea that grues have such an aversion to light that no one has ever seen one and it is impossible to gain a firsthand physical description of one and that, conversely, grues are such formidable predators that light is the only possible means of avoiding them. Neither of these ideas held absolutely true throughout the entire Infocom line of games. For instance, the game Sorcerer, which provided a wide variety of humorous responses to creative uses of magic spells, allowed the player to cast the Frotz spell on a grue, causing a "horrible, multi-fanged creature" from just outside the range of vision to run through the room "gurgling in agony and tearing at its fur". The game similarly provided a potion that granted the ability to see in darkness as a trap for players who forgot that the main purpose of a light source in the Zork games is not to preserve one's own vision but to repel grues; taking the night vision potion and turning off one's light source results in the almost immediate sight of, and subsequent devouring by, a grue. Near the end of the game, it is revealed that the main villain's plot for conquering the world involves manufacturing an army of light-resistant grues using a conveniently provided Frobozz Magic Company device.
As time went on the games became increasingly bold in their treatment of grues — Wishbringer allows the player to stumble upon a baby grue and get a good look at it before its parents return (described as a "horrid little beast with red eyes and slavering fangs"). (Zork: The Undiscovered Underground, a freeware game that was released 12 years later, incorrectly states that the character in that game is the first person to see a grue.) Spellbreaker, which had the player traveling through magical planes that represented various elements and principles, had the plane of darkness almost entirely populated by grues and forced the player to survive by using magic to take the form of one of the beasts.
One of the repeated references in Zork's backstory was to the ancient king Entharion the Wise and the legendary blade Grueslayer, which he used to directly fight grues in combat; this feat would not be repeated until the interactive fiction/RPG hybrid Beyond Zork, which allows a player who has advanced sufficiently in level and acquired certain items to boldly walk into the dark and kill grues that attack. (This feat required the acquisition of the Pheehelm, a device that boosted the player's intelligence and allowed him or her to sense the grues' movements telepathically without seeing them.) Finally, the modern-day game Zork: The Undiscovered Underground created as a promotion for Zork Grand Inquisitor featured an extended reference to a line in Zork III about "a whole convention of grues" in a certain location, by having the player infiltrate a literal grue convention, complete with lectures, entertainment and souvenirs.
That game was the first to give a detailed description of how grues looked, having the player disguise himself as a grue after seeing one and noting that it had a "fish-mouthed head, razor-sharp claws and glowing fur all over". (The reference to light-hating grues themselves glowing appears to be a mistaken interpretation of Sorcerer describing a grue glowing after a light spell has been cast on it -- although Spellbreaker does mention that grues' eyes give off a very small amount of light that lets them navigate in darkness.) However, an actual illustration of a grue had been seen previously, although in an obscure source -- one of Steve Meretzky's Zork gamebooks purposely included a section where the protagonists see a grue face-to-face before being eaten by it, presumably as a way to make the book attractive to Zork fans. Presumably these are not the only instances in the Zork games when grues have been seen — one event in Sorcerer has the player finding a Frobozz Magic Company "anti-grue kit" (admittedly a secret, experimental prototype) that contains a grue costume, with which the player can don and travel among grues unharmed. (The player in Zork: The Undiscovered Underground replicates this feat, albeit imperfectly.)
This is part of the running gag of a series of mostly failed attempts to find some sort of alternate means of protection against grues in the event one's light source fails, most famously in Zork II where a can of Frobozz Magic Grue Repellent was included as a red herring — mostly useless, since it would only last for one game turn after one's light source expired, during which the player couldn't see his location anyway. (In some versions of the game, however, it can be used as an alternate solution to one puzzle.) In Zork III the Magic Grue Repellent functions more like the player might expect, and lasts for several turns.
The actual reason light acts as such a potent Achilles' heel for grues is inconsistently given — some games imply that grues find levels of light ordinary for humans to be intolerably, blindingly painful but can nonetheless survive it (such as in Planetfall, where an obviously grue-like creature exists in a lit laboratory, "squinting and cursing at the light"). Zork: The Undiscovered Underground goes to the other extreme, having a grue caught in the light spontaneously combust on the spot. This latter explanation seems closer to the canon established by the main Infocom game series, since in Spellbreaker, if the player is shapeshifted into a grue and remains in a lit area for too long the light eventually kills him (and it is implied that the amount of light to which he is exposed is so faint as to be invisible to human eyes).
The question of how grues are able to survive undetected at all without being trapped in a dead end by a wandering human with a lantern has often been debated by fans, attributed either to their ability to squeeze through tunnels humans can't see or to use something akin to Dungeons & Dragons' "shadow jump" ability.
The modern graphical adventure games in the Zork series continue references to grues, with gurgling and growling grue sound effects audible in most shadowy or gloomy places and many points at which players can meet a gruesome death by wandering without light. A possible parody of the concept appeared in one puzzle in Return To Zork, in which the player was in danger of being killed by a grue after turning the light off in their own bedroom in a hotel; the only solution is to place a piece of lightly glowing, magical rock on the nightstand, providing just enough light to ward off grues while still making it possible to sleep. The in-jokes continue as well, with Zork Nemesis continuing a running gag about failed attempts to capture or domesticate grues by including in a library a book, "Interview with a Grue", that sported an illustration captioned "The Grue In Its Natural Habitat" (a blank black square). Zork Grand Inquisitor added to grue trivia the idea of the game "Grue, Fire, Water", a variant of Rock, Paper, Scissors wherein "Grue drinks water, water douses fire, and fire scares grue."
In the fourth Zork game, Beyond Zork, an evil being called an "Ur-grue" is introduced as the primary villain. Though similar in name, the Ur-grue is significantly different from the classic grue, being more akin to an evil god of darkness than a simple predatory monster.
Grues make an appearance in the Dungeons & Dragons RPG, appearing as a species of intelligent, evil elementals from the Inner Planes, presented as an alternative to the usual neutral, nonsentient summonable elementals of D&D. Aside from a reference to their being "born in places of darkness" on the Inner Planes and a general sense of shapeless menace, they have very little in common with their Infocom namesakes, despite having been introduced soon after the first Zork games and presumably having been inspired by them. They reappear as vicious creatures which attack PCs from out of the dark, the portrait of a Grue in the monster manual shows the creature with a bloody mouth full of knife-like fangs, presumably having just eaten an adventurer. The same creature also existed in the Gateway Bestiary, written for the second edition of the game, but was not at that time given the name "Grue".
Grues show up repeatedly in the roguelike game Ancient Domains of Mystery; originally only existing as an in-joke, "You are likely to be eaten by a grue" being one of the stock phrases one can encounter while traveling through the dark, eventually the classic Zork "lurking grue" was added to the game. Present in the dungeons but very rare, someone who is suffering under a serious bad-luck curse ("doomed") has a chance of being "eaten by a grue" at any time while moving through the dark. "Elemental grues" were also introduced as actual, very high-level monsters one could fight, in the style of the D&D grues.
In their original reference, in Jack Vance's Dying Earth series, grues are described as being part "ocular bat", part "uncanny hoon" and part man.