This is episode one of three in the "Commander Keen: Invasion of the Vorticons" saga. Part two is Commander Keen 2: The Earth Explodes (1990) and third and final game in the 'Vorticons' saga is: Commander Keen 3: Keen Must Die! (1990)
Tom hall and john Romero confirmed that William Joseph "BJ" Blazkowicz(the protagonist of wolfenstien is the grandfather of commander keen,commander keen is doom guy's father so they are all related to each other.