Akalabeth: World of Doom /əˈkæləbɛθ/ is a role-playing video game that had a limited release in 1979 and was then published by California Pacific Computer Company for the Apple II in 1980. Richard Garriott designed the game as a hobbyist project, which is now recognized as one of the earliest known examples of a role-playing video game and as a predecessor of the Ultima series of games that started Garriott's career.

The game was made by then-teenaged Garriott in the BASIC programming language for the Apple II while living with his parents and attending high school in the Houston, Texas suburbs. Begun first as a school project during his Junior year using the school's mainframe system and Apple II computer, as well as another Apple II bought for him by his father, the game continually evolved over several years under the working title D&D with the help of his friends and regular Dungeons & Dragons partners who acted as play-testers. Development of the game began soon after his initial encounter with Apple computers in the summer of 1979. When the game reached version D&D28b later that year (where "28b" refers to the revision), he demoed the game - now renamed to Akalabeth - for his boss at Clear Lake City, Texas-area ComputerLand, who suggested he sell the game to the store's clientele. Garriott consented and briefly packaged and distributed the game inside Ziploc bags, along with a cover drawn by his mother, within the store, selling fewer than a dozen copies. His boss secretly sent the sixteenth copy to California Pacific Computer Company, who proved interested enough to contact Garriott about purchasing the rights and publishing the game. Garriott flew to California with his parents and signed a contract with California Pacific to give them the publishing rights. He would receive $5 for each copy of his game sold. The game ended up selling 30,000 copies, netting Garriott $150,000. California Pacific went bankrupt not long after the release of his next game, Ultima.

In creating Akalabeth, Garriott was primarily inspired by Dungeons & Dragons, for which he held weekly sessions in his parents' house while in high school; and the works of J. R. R. Tolkien, which he received from an in-law of his brother. The name derives from Tolkien's Akallabêth, part of The Silmarillion; though the game is not based on Tolkien's story. Also, while not explicitly stated, Akalabeth is seen as the first game of the Ultima series, a very popular and influential series of role-playing video games. It was, therefore, included as part of the 1998 Ultima Collection where it officially picked up the nickname Ultima 0. The version in the Collection added CGA colors and MIDI. It ran on DOS, making it the first official port of the game to any system other than the Apple II, though an unofficial, fan-made PC version had circulated on the Internet since late 1995.

In the original game, the last monster on the need-to-kill list is called "Balrog", exactly like the demonic monsters from The Lord of the Rings, and unlike the later name for the monster in the Ultima games, Balron.