Portal was an early Activision game which featured a detailed science fiction universe and unusually rich story telling for it's time.
Conceived in 1984 by writer Rob Swigart and producer Brad Fregger, the game wasn't a traditional interactive fiction as it simulated the graphical interface of a futuristic computer terminal which gave the player access to a fictional global computer network named the WorldNet that predated the invention of the World Wide Web.
In Portal the player assumes the character of an astronaut who has returned from a failed, century long voyage through interstellar space to find the Earth devoid of human life and the remnants of civilisation decaying through neglect.
Discovering a working terminal amongst the ruins the player logs into the WorldNet, the global network that recorded all human activities.
The game centres around gathering fragments of information from various databases in the WorldNet covering topics such as history, military data and the social backgrounds of individuals. An artificial intelligence named Homer aids the player in creating a story from these fragments and acts as the games only NPC. Gradually you uncover the story of a boy named Peter Devore and the mystery of the eponymous portal.
A novel Portal: A Dataspace Retrieval by Rob Swigart (who also wrote the game) was published in 1988 and contained most of the text of the game as the player would experience it.