Commander Keen in Invasion of the Vorticons: Keen Must Die! (1990)

Commander Keen's very first adventure, and the debut of id's groundbreaking side-scrolling technology. In the game you play the role of Commander Keen: the alter-ego of an eight year-old genius by the name of Billy Blaze. When Billy learns that the Earth is in danger, he dons his brother's football helmet and his homemade interstellar spaceship to become Commander Keen -- Defender of the Earth!