Rutan

The Rutan Host are a race of amorphous green blobs. They have only appeared so far in Horror of Fang Rock, but are mentioned by the Sontarans in other serials.

Physical characteristics
The Rutan host (singular Rutan) are shaped somewhat like a jellyfish, with a green, glowing body and many light-green tendrils. These tendrils have surprising strength and they can climb walls with them. Rutan host can control and absorb electricity, which they can then use for defense and attack. A Rutan can kill a human with their bio-electricity. Rutans can see through some unknown organ, but their vision is blurred and green-tinted. Rutan speak in second person, which would imply a sort of hive mind. Rutan host can also shapeshift into other forms, but they need to know this form very well, usually after careful study and dissection.

Rutan host are amphibious and native to a cold planet (Ruta III). They have trouble dealing with climates unlike the ones on Ruta III, such as in warm environments.

Technology
Rutans have not shown much advanced technology due to their singular appearance. The Rutan scout in Horror of Fang Rock didn't use any advanced technology, though it apparently had some dissection tools. Rutan spaceships are crystalline in structure and seem to be large, glowing orbs.

History
The Rutan Host is engaged in a destructive war with the Sontarans and has been for thousands of years. They are constantly searching out new ways to win the war. It's unknown what started this conflict, but this war has driven both cultures. In the early 1900s, the Rutan Host was apparently losing this war.

Major appearances
Television episodes
 * Horror of Fang Rock
 * Referenced in The Time Warrior
 * Referenced in The Sontaran Experiment
 * Referenced in The Invasion of Time
 * Referenced in The Two Doctors

Original novels
 * Shakedown