Commander Keen (real name: Billy Blaze) is a character from a series of eponymous platform games by id Software. An incarnation of 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 kill the four hanged Keens to trigger the door that hides the switch.
When killed, a Commander Keen emits an electronically-distorted death cry as he falls off his hanging rope to the ground, his eyes wide open facing the player with a horrified look, middle body torn apart showing bloodied organs and ribcages, but his head and blood-soaked tennis shoes are clearly left intact. The horrified face Keen displays when killed is the one you see on Billy when he flies out of the level upon losing a life in the original Commander Keen games.
The Commander Keen can be considered a monster in the technical sense as he counts towards the kills percentage, will respawn under the corresponding settings, and is not included when the -nomonsters parameter is used. He does not, however, pose any threat to the player as true monsters do meaning he cannot attack the player.
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 Keens are injured and killed, respectively. When all the Keens in a map are killed, any sectors tagged 666 will open as doors.
- According to John Romero, the hanged Commander Keens were Adrian Carmack's idea and execution. Preferring to work on dark and gory themes, he had his revenge against the cute character he had to "endure" working with previously.
- The phrase in the prologue for Level 32: Grosse contains a reference to Keen's name, Billy Blaze: Congratulations, you've found the super-secret level! You'd better blaze through this one!
- The sounds used for the Keens are taken from the original Commander Keen games in that the Commander Keen "level start" sound plays when you kill them and the "raygun" sound plays when you damage them. The graphics used are a combination of original graphics and slightly modified Keen graphics from Commander Keen IV.
- Billy Blaze (legal name: William Joseph Blazkowicz II) is the grandson of Wolfenstein 3D's William Joseph "BJ" Blazkowicz according to The Official Hint Manual for Wolfenstein 3-D. The Doomguy is also implied to be a descendant of BJ in Wolfenstein RPG, though his exact relation to the other protagonists is unknown.
- In an early version of Brutal Doom, Commander Keen's head is replaced with that of pop singer Justin Bieber. When killed, the head just falls to the ground without any effects, although they still use the original sounds when injured or killed. Keen was changed back to normal as of v0.19.
The IWADs contain the following numbers of hanged Commander Keens:
|Game||ITYTD and HNTR||HMP||UV and NM|
|Monsters from Doom and Doom II|