"Commander Keen is a series of video games developed by id Software in the early 1990s. The series focuses on the adventures of Billy Blaze, an 8-year old boy who travels through space and assumes the identity "Commander Keen". The cartoon-style platform games are notable for their pioneering use of EGA graphics and shareware distribution.
Seven official Commander Keen games were released for the PC under MS-DOS. They are divided in mini-series, and are considered "episodes" of the full series. The eighth game in the series is available exclusively for the Game Boy Color."
Source: Wikipedia, "Commander_Keen", available under the CC-BY-SA License.