The Krug are a peculiar race that evolved on a warm, lush planet called Zheer. Zheer is a large planet with 1.3 times the mass of Earth and 1.1 times its gravity, has 3 big moons and is located in the Large Magellanic Cloud, one of the satellite galaxies in the vicinity of the Milky Way. Zheer's surface is covered in a dense jungle canopy, teeming with various life.
The Krug themselves are a race of parasites. Their appearance is similar to that of a small, pale eel, although they do not dwell in water, nor have anything to do with aquatic environments. Their body has two marble-like swellings in the middle of their body, one is their stomach, the other is their brain, which is, dispite its size, highly intelligent due to improved density and efficiency.
The Krug have two mouths, one on each end of its body. On demand they extrude small but very tough strings that puncture through soft tissues and connect to the central nerve system of their victim. From then on, they can send directed pulses of electricity and thus control the victim like a puppet, to very complex levels, including even involuntary functions, such as heartbeat in creatures with a heart. In turn, they can also connect to the appropriate nerves that convey sensory information from the victim. The victim remains aware of what is happening at all times, but his control over his own body is superceded.
The other set of strings, in the Krug's other mouth, is used to extract fat or other useful nutrients from the victim. The Krug are surprisingly adaptable and there are very few lifeforms that cannot be used as a host, although their control over life forms not native to their planet can be incomplete (for example, when latched onto a human they have difficulties with temperature-related functions, since warm-blooded creatures have evolved almost exclusively on Earth only).
The Krug have used various hosts native to their planet throughtout their history, and the prefference of hosts in various Krug circles was often the cause of ideological differences, and indeed war. Among the hosts they used were also animals with sensitive appendages, suited for the manipulation of tools. It is not entirely clear how and why they developed sentience, and later technology, but even though their rate of advancement was slow compared to galactic standards they have eventually reached the state of an interstellar empire.
They have encountered few habitable planets with native populations - sentient or otherwise. Their first encounter with intellectually and technologically equal (or, more precisely, superior) opponents was when they stumbled upon the Nec'Toom. The Nec'Toom at the time were spreading their territory in the Large Magellanic Cloud, colonizing one planet after another. Their homeworld was located on the fringes of the Cloud, and their colonization efforts were concentrated both in the Cloud and in the much larger neighbour, the Milky Way.
At first the Krug and the Nec'Toom tried to ignore each other, but in a few decades it was clear that war was inevitable due to their territorial conflicts. The Krug have managed to deliver some serious initial losses to their rivals dispite their serious technological inferiority, but soon the Krug started to encounter more frequent and more powerful Nec'Toom forces, and began to die by the thousands.
The Krug didn't know that these lethal reinforcements were the result of a diversion of forces from the Milky Way colonization project. In turn, this has allowed the Terrans, who in the meantime were engaging the Nec'Toom in the Milky Way, some breathing space. It wasn't that long before the Krug, who were by this point desparately using every dirty trick they could muster in order to at least delay the Nec'Toom advance, encountered a new alien vessel - a Terran ambassador ship. Soon, the Terrans and the Krug combined their efforts and opened up a large two-front war on the Nec'Toom.
The Magellanic War was bloody and difficult, because the Nec'Toom were still holding most of the vital cards, including the much vaunted technological superiority. However, the Terrans were now united, both with the Krug and with each other, and the industrial capacity of this alliance has managed to exceed that of the Nec'Toom. The end result was a complete and total, if very difficult and costly, victory for the Terrans and Krug. This partnership was only the beginning, and the war formed the basis of fruitful relationships between the Terrans and the parasitic Krug for many centuries to come.
Common Krug Hosts
The Br'dell are non-sentient creatures with cattle-like mentality native to Zheer, that were used by the Krug as hosts from before the beginning of their recorded history, because of their sensitive, flexible appendages that were suited for efficient tool-making. To this day, the Br'dell is one of the most popular hosts for the Krug to use, and when a Terran thinks of the Krug he often imagines a Br'dell before the true eel-shaped form of a Krug comes to his mind.
The Br'dell have five legs, distributed with equall spacing along their pancake-shaped body, with the odd, fifth leg being in the creature's front. The legs themselves are massive and peculiar, ending in hard dark-colored pointed "hooves" , and generally look like an insect's legs. The creature does not have any head, the only primary parts are the grey-colored, smooth body and the legs. From the creatures back there are two large fins that curve backwards and extend three meters upwards. The fin is attached to an easily discernible bone ridge, that becomes thinner and thinner towards its end, until it smoothly becomes an antenna that ends in a tiny brush. This brush collects moisture and aerial plankton that permeates the swamps that are these creature's natural habitat. On its belly, the creature has three thin tongue-like tentacles that split into three ends each on the very end. They are red in color and are very flexible, they serve these creatures to manipulate objects.
The creature masses at approximately one ton, and is, understandably, a very large critter.
Ever since the Krug/Terran victory in the Magellanic War, the Krug were left to occupy the Nec'Tooms capital planet, Krell. The surviving Nec'Toom were not left in peace, they were forced to be used as hosts for the Krug, and soon became pretty popular hosts, as their semihumanoid shape made it easier for the Krug to walk around in Human-designed ships and cities and prevented such unpleasant situations as trying to squeeze a huge Br'dell body through a Terran doorway. Presumably the poor Nec'Toom hosts don't enjoy being puppets, prisoners in their own bodies, but after the tremendous casualties and pains they caused in the war, nobody cares.
Some centuries after the Magellanic War was fought, the Krug have started a covert invasion of a primitive civilization in the Milky Way galaxy. They took control over several important leading figures in Arrunian society, and soon, entire villages were under Krug control with nothing more than frightening rumors reaching the rest of the population, like in some cheap second era scifi novel. The Terrans, who knew about this endeavor, turned a blind eye and ignored this invasion completely. Soon, the Arrun, who before the invasion were moving at a fast pace towards discovering nuclear power within a couple of centuries, were all completely enslaved to the Krug.
Physiologically, the Arrun somewhat resemble a reptilian version of a centipede/scorpion cross, with an elongated, multilegged body (green, with scales) that splits into two tails at the end, each of which is equipped with a poisonous sting, and two small pincers in front, as well as two appendages with fingers and thumbs. These guys mass about 100 kilos.