The Rutans, have long been at war with the Sontaran Empire, and this war dominates both cultures to the exclusion of all else. The Rutans only appeared on television in the serial Horror of Fang Rock , in which a single Rutan is encountered, though they are mentioned in some serials featuring the Sontarans.
In their natural forms, Rutans resemble large green Jellyfish, glowing blobs of biomatter with long ropey tentacles. They are amphibious and can cling to sheer vertical surfaces, with considerable mobility out of the water despite their shape. Rutans can also generate lethal electrical shocks which they use to kill, and seem to be able to absorb electricity directly from any source for there own energy instead of eating, sleeping, drinking etc. They reproduce by splitting them selves into two seperate organisms without having any loss in size, mass, volume etc. Rutans can speak, although the exact mechanism by which this works is unknown as they seem to lack mouths. The Rutan observed in Horror of Fang Rock spoke with a harsh, tinny male voice.
The title "Rutan Host" implies a group intelligence of some kind, and indeed Rutans never refer to themselves as individuals, therefore use first person plurals like "we", "us" and "our(s)". Rutans are able to operate independently (and like the Sontarans, often dispatch scout units consisting of a single soldier), but they do not see individuals as important and all individual desires are counted less important by the general desire to win the war with the "Sontaran rabble".
Rutans have also developed advanced shape-shifting technology, allowing them to appear in any form they wish. They often use this technology to adapt to alien environments and infiltrate alien cultures; Rutans are consummate spies. A Rutan usually kills specific individuals and then impersonate them, this tactic is to prevent discovery and to examine the individual more closely for a more accurate clone.
Horror of Fang Rock(1977): The cursed island of Fang Rock off the south coast of England is a place of rumour and tales of beasts from the sea. Three lighthouse men at the turn of the century face their fears when something comes in from the sea which brings death to all it touches.