Ghymnon

Ghymnon was a sentient acellular pathogen that was the sole inhabitant of the Unknown Regions planet Uokara. For millions of years, the pathogen covered the planet and killed thousands who attempted to conquer it. During the Imperial Era, the Sith Lord Darth Vader surveyed the planet for the Galactic Empire, but failed to detected the presence of Ghymnon, who infected the Sith via his respirator.

During quarantine in a bacta tank, Vader passed out and was confronted by Ghymnon in a hallucination that was controlled by the pathogens focus and based on the Sith's fears. Ghymnon attacked Vader while chastising the invader and then cast him into a stream of fire, believing that this would kill the Sith's mind. Vader instead took control of the fire and used it to defeat the infection, expelling the pathogen's physical form through his eyes so that it was sterilized by bacta. The Sith then had range troopers eradicate Ghymnon from the surface of Uokara.

Text and facts from the “Ghymnon” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.