Commander Keen

Commander Keen is a character named Billy Blaze from a series of eponymous platform games by id Software. The character can be found in the super-secret Doom II map, Level 32: Grosse, as an easter egg. In the final room of that level four hanged Commander Keen bodies are suspended from ropes by their necks around a metal cube containing the exit switch. The player must destroy the four hanged Keens to trigger the door that hides the switch.

The Commander Keen can be considered a monster in the technical sense as it counts towards the kills percentage, will respawn under the corresponding settings, and is not included when the -nomonsters parameter is used. It does not, however, pose any threat to the player as the true monsters do.

Technical
Internally "KEEN" is used as a prefix for sprites relating to Commander Keen. The type of the object inside the source code is given the name "MT_KEEN". The sounds "DSKEENPN" and "DSKEENDT" are used when the Keen objects are injured and killed, respectively.