Marooned On Mars was originally released as a shareware program back when putting out a free episode of your game was common (it was also more common to have multi-episode games at the time); you could download it, test it, share it with friends... and hopefully it would have lured you into purchasing the other two episodes. This game introduced many features which became standard for all future Keen games, such as the pogo stick, the use of a Ray Gun, and the inclusion of the Vorticon Alphabet, which would become all the more relevant in later games. Unfortunately, you don't start out with any weaponry or the pogo stick; they all must be found, but once you get your hands on such glorious items, there will never be a need to hunt them down again... ever in a Keen game. They're yours to keep.

Another interesting factoid: Marooned On Mars was not the original plan for a new game. Instead, the programmers had actually made a close-to-carbon copy of the first level of Super Mario Bros. 3 as a guinea pig for smooth horizontal scrolling in a PC game, something that had never quite worked before. It worked, but Nintendo wasn't interested in perhaps creating a full PC version of one of their greatest hits to date. Their efforts DID catch the eye of Apogee Software, and together they set an agreement to use this new programming know-how for something new, which eventually became the first episode of Commander Keen.

The Earth Explodes was the first commercial episode of the series -- no more freebies for Keeners around the world. Episode II continues with the platforming gameplay methods from the previous episode, offering more wild and wacky levels featuring nasty Vorticon baddies, though you're now inside a spaceship. Development of this episode was rather rushed due to a rapid schedule to get all three episodes available at once. While the first episode was completed over the course of three months, the remaining two had to be completed within a matter of days. Nonetheless, Episode II required fewer fixes than the first episode.

As the final installment of the "Invasion of the Vorticons" trilogy, Episode III was also hastily produced, perhaps moreso than Episode II, which resulted in numerous bugs -- including a major flaw in one level which left players unable to complete it successfully. A patch had to be subsequently released to fix this and other glaring errors. It's still an interesting game to play, and my humble opinion, the most difficult Keen game of all time. One notable feature in Episode III is a complete translation of the Vorticon alphabet, hidden amongst all the Vorticon VI wilderness. If you manage to find it, be sure to write it down because it may help you understand writing in all the other Keen games. Episode III also introduced us to Mortimer McMire, Commander Keen's arch-nemesis with an extra IQ point (315 to Keen's meager 314) and one who wants Keen out of the picture for good. (You can guess what his role in this game is...)

Another nifty nugget of 'nfo: the original Commander Keen trilogy was once announced to be made available for a Nintendo console, though it's not clear whether it would have been the NES, SNES, or the Game Boy. It was even claimed on an Apogee Software promotional flyer that a "major American Nintendo publishing company" was ready to handle the release. However, such a hot plan never came to fruition, and Nintendo fans never received a Commander Keen game to call their own... well, not until about ten years later.