Commander Keen IV: Secret of the Oracle

Commander Keen in Goodbye, Galaxy (stylized as Goodbye, Galaxy!) is a two-part episodic side-scrolling platform video game developed by id Software and published by Apogee Software in 1991 for DOS. It consists of the fifth and sixth episodes of the Commander Keen series, though they are numbered as the fourth and fifth, as Commander Keen in Keen Dreams is not part of the main continuity. The game follows the titular Commander Keen, an eight-year-old child genius, as he first journeys through the Shadowlands to rescue the Gnosticenes so they may ask the Oracle how the Shikadi plan to destroy the galaxy, and then through the Shikadi's Armageddon Machine to stop them. The two episodes feature Keen running, jumping, and shooting through various levels while opposed by aliens, robots, and other hazards.

After the success of Commander Keen in Invasion of the Vorticons, the developers of the game, including programmers John Carmack and John Romero, designer Tom Hall, and artist Adrian Carmack, left their jobs at Softdisk to found id Software. After making a prototype game in Keen Dreams to develop new ideas such as gameplay changes, graphical enhancements, and artistic improvements, the team worked on making a sequel trilogy of episodes from June to December 1991. During development the last episode was split off to be released as a stand-alone game, Commander Keen in Aliens Ate My Babysitter, with the remaining two episodes produced as a pair instead of a trilogy.