Zork was an early text-only adventure game, though it wasn’t the first — that honor goes to Colossal Cave Adventure. Released in 1980, it delivered the player into an extraordinarily rich and vivid universe, despite its total lack of graphics.
To this day the opening lines induce waking hallucinations in old-school gamers:
You are standing in an open field west of a white house, with a boarded front door.
There is a small mailbox here.
What made Zork work, aside from its homespun, minimalist eloquence and self-referential wit (it was full of sly references to, among other things, Colossal Cave Adventure), was its eerily advanced text parser, which accepted commands from the player in plain English and turned them into actions in the game.
Zork’s influence on later adventure games can’t be overstated — as an homage, the entirety of Zork was inserted into Call of Duty: Black Ops as an Easter Egg.