The Realm of Angbar by Elfstone

The fictional history of the Realm of Angbar is eaccessible from the main screen. Here's a summary: the narrator is named Elfstone (also the programmer's alias). Elfstone says that a little known evil priesthood has set up a huge temple in the heart of Elfhelm. They worship the evil Wormlord. You job is to invade the temple and slay the Wormlord. Elfstone goes ahead and tells us that this adventure series is brought to us by Share Data, and that your character can move around to other disks in the Realm of Angbar, such as Quest of the Dragon's Run, The Mountain-Lord of Eriath, Fangwood, and The Crystal Realm. [Unfortunately these disks were never published.]

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For the record, the game does not end if you kill Wormlord. Long before Worlds of Warcraft, Elfhelm's Bane is a game that doesn't end.