During its 1980s heyday, commercial versions of Zork released for personal computers sold more than 800,000 copies. Today, unofficial versions of the game can be played online, on smartphones, and on Amazon Echo devices, and Zork is inspiring young technologists well beyond the gaming field.

It’s an impressive legacy for a project described by its developers as a hobby, a lark, and a “good hack.” Here’s the story of Zork’s creation, as recounted by its four inventors—and a look at its ongoing impact.

Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling—who between them earned seven MIT degrees in electrical engineering and computer science, political science, and biology—bonded over their interest in computer games, then in their infancy, as they worked or consulted for the Laboratory for Computer Science’s Dynamic Modeling Group. By day, all of them but Blank (who was in medical school) developed software for the U.S. Department of Defense’s Advanced Research Projects Agency (DARPA), which funded projects at MIT. On nights and weekends, they used their coding skills—and mainframe access—to work on Zork.

In early 1977, a text-only game called Colossal Cave Adventure—originally written by MIT grad Will Crowther—was tweaked and distributed over the Arpanet by a Stanford graduate student. “The four of us spent a lot of time trying to solve Adventure,” says Lebling. “And when we finally did, we said, ‘That was pretty good, but we could do a better job.’”

By June, they’d devised many of Zork’s core features and building blocks, including a word parser that took words the players typed and translated them into commands the game could process and respond to, propelling the story forward. The parser, which the group continued to fine-tune, allowed Zork to understand far more words than previous games, including adjectives, conjunctions, prepositions, and compound verbs. That meant Zork could support intricate puzzles, such as one that let players obtain a key by sliding paper under a door, pushing the key out of the lock so it would drop onto the paper, and retrieving the paper. The parser also let players input sentences like “Take all but rug” to scoop up multiple treasures, rather than making them type “Take [object]” over and over.

Vibrant, witty writing set Zork apart. It had no graphics, but lines like “Phosphorescent mosses, fed by a trickle of water from some unseen source above, make [the crystal grotto] glow and sparkle with every color of the rainbow” helped players envision the “Great Underground Empire” they were exploring as they brandished such weapons as glowing “Elvish swords.” “We played with language just like we played with computers,” says Daniels. Wordplay also cropped up in irreverent character names such as “Lord Dimwit Flathead the Excessive” and “The Wizard of Frobozz.”

Within weeks of its creation, Zork’s clever writing and inventive puzzles attracted players from across the U.S. and England. “The MIT machines were a nerd magnet for kids who had access to the Arpanet,” says Anderson. “They would see someone running something called Zork, rummage around in the MIT file system, find and play the game, and tell their friends.” The MIT mainframe operating system (called ITS) let Zork’s creators remotely watch users type in real time, which revealed common mistakes. “If we found a lot of people using a word the game didn’t support, we would add it as a synonym,” says Daniels.

The four kept refining and expanding Zork until February 1979. A few months later, three of them, plus seven other Dynamic Modeling Group members, founded the software company Infocom. Its first product: a modified version of Zork, split into three parts, released over three years, to fit PCs’ limited memory size and processing power.

Nearly 40 years later, those PC games, which ran on everything from the Apple II to the Commodore 64 in their 1980s heyday, are available online—and still inspire technologists. Ben Brown, founder and CEO of Howdy.ai, says Zork helped him design AI-powered chatbots. “Zork is a narrative, but embedded within it are clues about how the user can interact with and affect the story,” he says. “It’s a good model for how chatbots should teach users how to respond to and use commands without being heavy-handed and repetitive.” For example, the line “You are in a dark and quite creepy crawlway with passages leaving to the north, east, south, and southwest” hints to players that they must choose a direction to move, but it doesn’t make those instructions as explicit as actually telling them, “Type ‘north,’ ‘east,’ ‘south,’ or ‘southwest.’” Brown’s chatbot, Howdy, operates similarly, using bold and highlighted fonts to draw attention to keywords, like “check in,” and “schedule,” that people can use to communicate with the bot.

Jessica Brillhart, a filmmaker who creates virtual-reality videos, also cites Zork as an influence: “It provides a great way to script immersive experiences and shows how to craft a full universe for people to explore.”

Zork creator Dave Lebling created this hand-drawn map of the game’s “Great Underground Empire” in the late 1970s. The GUE, as it was known, was full of interesting things to explore, including an ancient temple, a volcano, and a wizard’s workshop. RICK THORNQUIST, COURTESY OF DAVE LEBLING

A printout of the game’s source code from November 1981. The original version of Zork was written on a Digital Equipment Corporation PDP-10 mainframe that ran an operating system called ITS and a programming language called MDL—both developed at MIT. Commercial versions of the game were written in a programming language called Zork Implementation Language (ZIL) that ran within a virtual machine on top of personal computers. Courtesy of Mike Dornbrook

This snippet of code, written in ZIL, is an example of the way Zork handled verbs that players typed to propel the game forward. Specifically, it shows the default code that can be activated when a player tries to unlock something in the game. Inputting “Unlock” when confronted with a locked grate could yield the responses “The grate is unlocked” or “You can’t reach the lock from here” or “It doesn’t seem to work,” depending on the player’s possessions and location. COURTESY OF MIKE DORNBROOK

In 1979 a group of 10 MIT alumni and professors, including three of Zork’s four original creators, founded a software company called Infocom. The following year, Infocom licensed Zork to a company called Personal Software, which distributed the first commercial version. Because the original version of Zork was too large to fit on the home computers available at the time, the game was split into three parts, which were released separately. This was Part I. COURTESY OF MIKE DORNBROOK

In 1981, Infocom reacquired the rights to Zork from Personal Software and redesigned the game’s packaging. The new look used letters carved in stone and a trapdoor to evoke a sense of mystery and reference Zork’s caves and dungeons. COURTESY OF MIKE DORNBROOK

Realizing that Zork players wanted—and would pay for—accessories like maps, Infocom started selling game merchandise, which it delivered by mail. In October 1981, an MIT grad named Mike Dornbrook took over that business as part of a company he called the Zork Users Group. These maps date from 1981 and 1982. COURTESY OF MIKE DORNBROOK

Dornbrook also started a newsletter for Zork players, called “The New Zork Times.” The witty publication, which came out approximately four times a year, carried a range of news about Infocom games. COURTESY OF MIKE DORNBROOK

In 1982, Dornbrook created a series of Zork hint books called InvisiClues. The books helped players crack the game’s puzzles, but they were printed in invisible ink to prevent people from learning all of Zork’s secrets at once (special markers were provided to reveal the clues). The following year, Dornbrook sold his Zork Users Group business to Infocom and joined the company. COURTESY OF MIKE DORNBROOK

Infocom later released a “trilogy” version of Zork that combined disks for all three parts of the original game. The packaging included several bonus items related to the game’s fictional world, such as brochures for resorts located in Zork’s Great Underground Empire and a coin known as a Zorkmid. COURTESY OF MIKE DORNBROOK

By 1984, Zork had sold so well that Infocom ran a magazine ad boasting about the game’s popularity. The ad said that Zork I had been “a best-seller ever since 1981” and was the top seller on [software distributor] Softsel’s 1983 list of recreational software. COURTESY OF MIKE DORNBROOK