Tir Na Nog is a video game published in 1984 by Gargoyle Games for the ZX Spectrum and Amstrad CPC. It was ported to the Commodore 64 in 1985. It is loosely based on Celtic mythology.
The game was widely positively received by the gaming media. The game forms part of an unofficial trilogy with the science fiction title Marsport and Dun Darach. Marsport has little to do with Tir Na Nog aside from the similar game styles. Dun Darach, however, is a proper part of the same story as Tir Na Nog.
The game has many features that were groundbreaking in 1984 such as a large central character, animated backgrounds and parallax scrolling.
Source: Wikipedia, "Tir Na Nog (video game)", available under the CC-BY-SA License.