(From the NetHack 3.4.1 source code):
"Quasits are small, evil creatures, related to imps. Their talons release a very toxic poison when used in an attack."
"They say that a blessed tin of quasit meat is a quick meal."

Hunting the Quasit

Quasits do not appear in "real" mythology, instead arising as the creation of a game designer in the early 1980's. Since then, numerous computer games and fantasy roleplaying systems, including Dungeons & Dragons, have mentioned this creature.

To establish a lower bound on the creation of the quasit, we examine two key games, which influenced (and inspired, by many of the various authors' admissions) all other games referenced in this essay.

First, The Colossal Cave Adventure, a simple text adventure from 1975 (give or take a year according to Will Crowther, the author), all but created the genre of fantasy-oriented computer games. It did not include any quasits, however.

In 1979, Automated Simulations (later called Epyx) released "Temple of Apshai," which arguably counts as the first of the "Rogue-like" games. It did not contain any mention of quasits either.

So, tracing backward from the known inclusion of the quasit in NetHack, we find that the earliest existent version of Hack (predecessor to Nethack), v1.0.1 from April of 1985, already had the elusive quasit as a monster.

Hack evolved from an older game called "Rogue". Rogue spawned a number of similar games, of which Hack and The Dungeons of Moria gained the most popularity.

Before moving on to Rogue itself, an examination of Robert Alan Koeneke's Moria, reveals its use of the quasit as of v4.7, from March of 1987. However, as no earlier versions remain, this does not provide much information. At the earliest however, the presence of a quasit in Moria could have come from the first release, in March of 1983. This would predate Hack.

Finally moving along to Rogue itself, the earliest source code readily available (Jon Lane's PC port) comes from 1984(?), and does not include a quasit. Nor does the initial BSD (4.2) version, 5.3, from April of 1983.

Complicating matters, releases of Rogue produced chronologically later, but with lower version numbers, such as v1.7 for CP/M from 1990(?), and the 3.6.1 "rogue restoration" project, do include the quasit. Painfully tracking down a copy of the v3.6 source code for Rogue, dated June of 1981, we discover that it includes our quasit!

Finally, an bit of commentary from Glenn R. Wichman, the least well known of Rogue's authors (for the same reason that the quasit hid its origins so well), explains the situation:
We had a playable game, without all the features yet (e.g., no armor), when Michael transferred to U.C. Berkeley, where he met up with Ken Arnold. For a while, we each moved forward with our own versions of the game, him in Berkeley and me in Santa Cruz. This proved to be too difficult to keep up logistically, so I just let Michael & Ken take over Rogue development completely. To this day, there are a lot of folks who think of it as Michael & Ken's game.

The answer finally emerges from the confusion. The quasit did originate in Rogue, but ceased to exist for several years when Wichman abandoned his version of the code. If not for Hack and Moria, presumeably inspired by versions of Rogue prior to its three authors parting ways, we would not currently have a mythical monster known as a quasit.