Swordquest is an unfinished series of video games produced by Atari, Inc. in the 1980s as part of a contest, consisting of three finished games and a planned but never released fourth game. All of the games came with a comic book that explained the plot, as well as containing part of the solution to a major puzzle that had to be solved to win the contest. Each game had essentially the same gameplay: Logic puzzle adventure style gaming interspersed with arcade style action gaming. The character wanders through each screen, picking up and dropping items, playing simplified variants of current 'twitch' games of the time between screens. If the correct items are placed in a room, a clue shows up, pointing the player to a page and panel in the comic book included with the game. There, the player would find a word that was hidden in that panel. If the player found all five correct clues, amongst all the hidden words (hinted by a hidden clue in the comic), they could send the sentence to Atari and have a chance to compete in the finals and win a prize. Earthworld was the first of the four games. Its room structure was based on the signs of the zodiac.

The games follow twins named Tarra and Torr. Their parents were slain by King Tyrannus's guards, prompted by a prophecy by the king's wizard Konjuro that the twins would slay Tyrannus. The twins were then raised as commoners by thieves to avoid being slain by the king. When they go to plunder Konjuro's sea keep, they accidentally reveal their identities to him. The twins then start running from a demon summoned to kill them, but it appears that a jewel they stole attracts it. After smashing the stone to avoid the demon, two of Tyrannus's old advisers appear and tell the two about the "Sword of Ultimate Sorcery" and the "Talisman of Penultimate Truth." They are then transported to Earthworld.