Many people regard Akalabeth: World of Doom as the spiritual predecessor of Ultima I. Wikipedia states that the game even made an Ultima Collection where it was nicknamed Ultima 0. Akalabeth is a for todays standards obviously crude dungeon crawler with wire-frame graphics that also boasted an above-world map on which the player moved around. Back then it was revolutionary and started the huge franchise that became Richard Garriott's Ultima series. Source: Wikipedia, "Akalabeth: World of Doom," available under the CC-BY-SA License.