The game follows the titular Commander Keen, an eight-year-old child genius, as he journeys through an alien world to rescue his kidnapped babysitter.

It did not sell as well as the first trilogy, which was attributed by id to poor marketing and its awkward status as a stand-alone retail game in a series known for groups of shareware episodes.

There are giant switches which must be jumped up into or dropped onto to flip which have effects on the gameworld, such as retracting and extending gates or initiate moving platforms.

In the game's introduction, eight-year-old child genius Billy Blaze is working on his wrist computer in his backyard clubhouse when his babysitter, Molly McMire, calls him in for dinner.

During the game, Keen journeys through the various outposts, factories, and installations of the alien Bloogs on the planet of Fribbulus Xax as well as a space station above it.

In October—December 1990, a team of employees from programming studio Softdisk, calling themselves Ideas from the Deep, developed the three-part video game Commander Keen in Invasion of the Vorticons.

Keen's red sneakers and Green Bay Packers football helmet were items Hall wore as a child, dead enemies left behind corpses due to his belief that child players should be taught that death had permanent consequences, and enemies were based loosely on his reading of Sigmund Freud's psychological theories, such as that of the id.

[2][3] The level maps were designed using a custom-made program called Tile Editor (TEd), which was first created for Dangerous Dave and was used for the entire Keen series as well as several other games.

[6] For Vorticons, Carmack had created adaptive tile refresh to produce a scrolling effect on computers not powerful enough to redraw the entire screen when the player moved.

By August they had completed a beta version of episode four, "Secret of the Oracle", and Romero sent it off to a fan he had met from Canada, Mark Rein, who had offered to play-test the game.

Within a few weeks of being hired, Rein made a deal to get id into the commercial market: to take the sixth episode and make it a stand-alone game, published as a retail title through FormGen instead of part of a shareware trilogy.

They signed the deal, but Scott Miller of Apogee was dismayed; he felt that not having a full trilogy for the shareware game would hurt sales.

[4] Aliens did not sell as well as hoped for by id, which the team partially blamed on what they felt was terrible box art produced by a company that had previously designed packaging for Lipton tea.

[11] A short review in the same issue as part of a listing of shareware games that could be ordered through the magazine called Aliens the "special edition" of the series and "the best one yet".

[3] Another trilogy of episodes, titled The Universe Is Toast, was planned for December 1992, but was cancelled after the success of id's Wolfenstein 3D and development focus on Doom.