Zork is a text adventure game first released in 1977 by developers Tim Anderson, Marc Blank, Bruce Daniels, and Dave Lebling for the PDP-10 mainframe computer.

Blank and Joel Berez created a way to run a smaller portion of Zork on several brands of microcomputer, letting them commercialize the game as Infocom's first products.

[3][6] In the first episode, or Zork I, a thief character is wandering the underground as well, taking items that have been left behind or even stealing from the player's possessions.

Long before the time the game is set in, the Quendor empire, having conquered everywhere above ground, built a massive cave complex to expand.

[11] Zork I begins with the unnamed player standing in an open field west of a white house, with a boarded front door; most of the game occurs underground, as do the subsequent episodes.

Once the player has all the items, they must feed an elderly man, who reveals himself as the Dungeon Master and shows them the doorway leading to the final hallway.

[8] They believed that their division's MDL programming language would be better suited for processing complex text inputs than the Fortran code used in Adventure.

[8][12] Zork's prototype was built for the Digital Equipment Corporation (DEC) PDP-10 mainframe computer, the only system that supported their programming language.

According to Anderson, "it took time for people to learn how to write good problems", and Lebling's first, uncomplex parser was only "almost as smart as Adventure's".

The group, referring to themselves as the "implementers", continued working on the game after Lebling returned, adding features and iterating on the parser through June 1977.

[15] The text responses to the player's commands were frequently opinionated and sarcastic, a design choice that mirrored the group's speaking patterns.

[19] No specific projects were initially agreed upon and Infocom had no paid employees, but discussions were focused on developing software for smaller mainframe computers.

[19][20] Blank and Joel Berez came up with a plan to make Zork work on personal microcomputers, which were then beginning to become popular and which would greatly expand the audience for the game.

Although microcomputers had very limited memory space compared to mainframe computers, they felt the project might be viable using floppy disks and a custom programming language if the game was cut into two pieces.

Infocom purchased a TRS-80 personal computer early in 1980, which could run the game after Blank and Scott Cutler created an interpreter program.

Infocom began preparing to release the first section under the title Zork: The Great Underground Empire – Part I. Mike Dornbrook, who had never played the game, tested it as an audience surrogate.

He felt that the game would be wildly successful and develop a cult following, and urged Infocom to produce tie-in products like maps, hints, and shirts.

The rest of the company was not convinced enough to start producing any such add-ons, but they did add an object in the game that gave an address for players to mail in for maps and hints in case it proved popular.

Since Personal Software declined to publish the 1979 PDP-11 version of the game, Infocom sold some copies earlier in the year after announcing it to PDP-11 user groups.

[20][21] Infocom eventually produced hint booklets with progressive answers to questions written in invisible ink, branded as InvisiClues.

[15] Marc Blank constructed Zork III and added gameplay changes such as the modified point system to move the game away from straightforward dungeon exploration.

[12] Zork II was offered to Personal Software in April 1981 and the contract was signed in June, but Infocom grew wary of continuing this relationship.

Rather than find another publisher, Infocom decided to self-publish its games and began renting office space and contracting with production facilities.

Infocom developed interpreters for the Commodore 64, Atari 8-bit computers, CP/M systems, and IBM PC compatibles, and released the episodes of Zork for them as well in 1982.

[27][28] Reviewers for Softalk and The Space Gamer enjoyed how the parser let them input more complex sentences than did earlier games, the Softalk review noting that every other game since Adventure had limited the player to two-word phrases, though they also thought players would largely stick with clearer two-word commands.

[28] Byte concluded that "no single advance in the science of Adventure has been as bold and exciting" as Zork, a sentiment echoed by Softalk.

[67][68] A reference to grues is also made in title and refrain of Nerdcore rapper MC Frontalot's song "It Is Pitch Dark".

[69] Writer Bernard Perron, while discussing horror in video games, stated that being hunted by a grue was a "terrifying situation no player had ever experienced before".

[81][82][83][84] A graphical port of Zork I for the PlayStation and Sega Saturn consoles was produced by Shōeisha in Japan in 1996, nineteen years after its original release.

[55] Four gamebooks, written by Infocom developer Steve Meretzky and set in the Zork world, were published in 1983–1984: The Forces of Krill (1983), The Malifestro Quest (1983), The Cavern of Doom (1983), and Conquest at Quendor (1984).