In earlier text adventures (now usually denoted as "interactive fiction", including retroactively) such as the original ADVENT (also known as Colossal Cave Adventure or simply Adventure), wandering around with no light source was extremely dangerous as -just like exploring a real cave- it was very possible to fall into an unseen crevasse and die. Zork retained the mechanic, but the traditional crevasse didn't work so well outside of the original cave setting. As Zork included houses and other such structures, they decided to assign the role to a monster that was conveniently afraid of light. Every time you move in a dark room, you have a chance of being instantly killed by the grue.
My older sister used to have a collected edition of all the Infocom adventures and it came with reprints of all the text that accompanied the original game, including all the history/backstory for the Zork saga collected into one book. The whole thing is a hilarious read, very witty and Pythonesque, though you have to hunt around to find all the bits these days.
http://infodoc.plover.net/manuals/zork1.pdfIn 659 GUE*, the Kingdom of Quendor was relatively small ... ascension of Duncanthrax to the throne of Quendor on the final day of 659... The conquest of Antharia also gave Duncanthrax possession of Anthariaís famed granola mines. Unfortunately, no one in Quendor liked granola. ... As Duncanthraxís invasion swept across the new lands, he made a startling discovery: huge caverns and tunnels, populated by gnomes, trolls and other magical races, all of whom loved granola.
So, the "Great Underground Empire" setting for the original Zork was conquered because the rising regional power needed to find a market for their excess breakfast cereal.
In 883, after countless years of decadence and over-taxation, The Great Underground Empire collapsed, the Royal Treasury was sacked and everyone moved somewhere else.
This was after they made the point that the Empire covered almost the entire world.
BTW the story continues in the manuals for the other Zork games.
http://infodoc.plover.net/manuals/zork2.pdfLOCAL GOVERNMENT: Antharia is ruled by a council of four Elders - one from the Shipbuilding Guild, one from the Granola Miners Guild, one from the Marble Cutters Guild, and one from a popular waterfront pub called "Emu's"
Infocom really did have high quality extras back in those days, full color manuals, well-written and entertaining.
EDIT: Each game's introductory section is framed in-universe as a different type of publication. Zork 1 was an elementary-school level history book, Zork 2 was a tourist brochure, and Zork 3 was a shareholder's report for FrobozzCo.
http://infodoc.plover.net/manuals/zork3.pdfThis is the relevant bit:
The Frobozz Magic Grue Repellent Company is one of FrobozzCo's fastest growing divisions. Sales of grue repellent nearly tripled last year, spurred on by drastic extensive improvements made in the product and by an aggressive marketing campaign. Magic Grue Repellent Company executives can proudly point to a 31% drop in grue-related deaths during the last year, and a consequent 31% drop in the grue population. The discovery of a particularly effective new additive by the Magic Grue Repellent Company's research division has increased the efficiency of the product by 45%. Studies have shown that most grues will not come within 70 feet of someone sprayed with New Improved Repellent. The new additive, dubbed G-17, is also longer-lasting, requiring fewer sprayings, and it can be made from ordinary sand!
The Magic Grue Repellent Company also increased the product line with the introduction of seven new odors of repellent, in addition to the regular old socks/burning rubber odor. The new odors include rotting eggs, dead fish, swamp gas, three-week-old meatloaf, gym locker, wet dog and mint. Several ingenious sales strategies were highly successful. The Free-Noseplugs-With-Every-Can campaign, in association with the Frobozz Magic Noseplugs Company, ran for one month and increased sales by 92%. Advertisements featuring grue-mangled corpses ran before and during the peak travel season. Finally, a joint packaging effort with the Frobozz Magic Lantern Company to produce a Frobozz Anti-Grue Kit paid off with remarkable end-of-year sales.
https://www.mocagh.org/infocom/beyondzork-lore.pdfDORNBEAST Smart adventurers run the other way when they hear "Hurumph," the battle cry of the deadly dornbeast. Its 69 sensitive eyes can paralyze an unwary explorer with a single glare. Captured victims are plastered with round, sticky secretions that never come off.
Edit
3. For completeness now I started poking around for the other good stuff. Pretty sure I found all the stuff I remember now:
This one's good because it has pictures of the various Flathead Dynasty members:
https://www.mocagh.org/infocom/zorkzero-calendar.pdfThese one are in the same setting, have a lot of the same aesthetics / artists involved:
https://www.mocagh.org/infocom/wishbringer-manual.pdfhttps://www.mocagh.org/infocom/enchanter-manual.pdfhttps://www.mocagh.org/infocom/sorcerer-manual.pdfhttps://www.mocagh.org/infocom/spellbreaker-manual.pdf