Gray Goo

The Gray Goo is the main villain (and playable character) of the video-game, Tasty Planet, it is based upon the theoretical doomsday super-organism of the same name and much like its potential real-life counterpart its sole purpose in life is to spread via devouring every living (and non-living) being into its nano-based form.

Unlike the theoretical entity however this Gray Goo seems to be fully independent with actual sapience rather than base instinct and the game employs fanciful notions such as digesting a time-travel machine, allowing the Gray Goo to travel across time itself and devour all life on Earth from the prehistoric age all the way up to the distant future.