While the fanatical Kraliens may be the most numerous and constant threat to the USFP, it is the Skaraans (Ska-RAY-ans) and their War Corporations that are the true enemies of peace in the known galaxy. They thrive on conflict between the races, eagerly encouraging border disputes, so all sides will come to the War Corporations for the latest weaponry, and the Skaraans carefully keep the sides in balance, so no one side can gain an advantage over any other.

Until the Terrans arrived on the scene, it is assumed the Skaraans had kept this balancing act going for millennia. Unfortunately, with the TSN entering the picture, our superior technology forced the Kraliens, Arvonians and Torgoth to band together. The Skaraans soon joined the fight, and proved to be (other than the Ximni) the only other race that matched us in terms of FTL technology and firepower. Apparently, the Skaraans had been holding back the best technology for themselves.

The Skaraan cruiser, (known colloquially as the Defiler) battleship (Enforcer) and dreadnought (Executor) are each about the size of a TSN warship, but are incredibly powerful for their size. They can be equipped with either Warp or Jump drive, although their use of this technology in combat is limited, and appears to have a very short range. Skaraan warships also carry a number of advanced modular devices, which can be used to cloak their ships from sensor detection, shoot down our torpedoes or mines, or disable our own Warp drive with a tractor beam. Since each Skaraan warship carries its own unique combination of these modular systems, this makes their tactics very unpredictable and dangerous. Skaraans also have a standard base station design, which serves as a particular War Corporation's regional headquarters.

Physically, a Skaraan is about the size of a donkey, and has four legs, two arms, and a muscular, prehensile tail that can also be used to operate equipment. A Skaraan's head is vaguely horse-like, but biologically Skaraans are not similar to any Earth animal. They appear to have evolved long ago in a different direction than other races in the galaxy, developing multiple limbs while still living in an aquatic environment.  While their biology is largely unknown to the TSN, it is believed that an individual Skaraan is actually a symbiosis between a male and female pair, who reproduce on a cycle of five to ten years. A Skaraan does not consider itself male or female, and often can seem to be conversing with itself, but the Skaraan still considers itself an individual. Skaraans do not form any kind of cultural or family bond, outside of the bond to the Corporation.

Not all Skaraan Corporations are War Corporations, but those Skaraans that are encountered by the TSN usually represent a War Corporation. While Skaraans do have a central government, it has no real power, and Skaraans have no real societal structure; their Corporations are their organizational and governing structure. Since all Corporations are in competition with one another, conflicts between Corporations are common, even to the point of open warfare. The Skaraans actually have no malevolent motive in keeping conflict going between the enemy races, and between the Hegemony and the TSN, their Corporations are simply selling to the highest bidder, with different corporations taking different sides in the conflict. The Skaraans have approached the TSN several times about selling us technology, but our charter with the USFP prohibits such deals, even if we were inclined to take them up on the offer.

Despite their warmongering traits, Skaraans are actually quite amiable and outgoing, and they are the only known race that has been seen mingling and interacting with all of the other races. They are adaptable and can survive in a wide variety of environments, meaning that the other races do not have to make adjustments to their life support systems when Skaraans visit.

From the Terran Stellar Naval Academy Tactical Manual:

An adult Skaraan body is about the size of a donkey. At the front is a centaur-like torso with two small arms and a horse-like head. At the rear is a muscular tail that can operate intricate controls.

The Skaraan central government exists only to enforce civil laws. It has no diplomats and makes no policies, treaties, or tariffs relating to non-Skaraan affairs. Skaraans conduct defense and interplanetary trade through private corporations. These corporations operate strictly for profit, and have a reputation for being sneaky. Skaraan War Corporations have offered their services to the USFP but so far we have never hired them.

While Skaraan vessels are built around a set of standard hulls, each War Corporation outfits its ships with different technologies, making the Skaraans tricky enemies full of surprises. Every Skaraan vessel is equipped with some combination of the following abilities:

Warp Drive (5 second bursts)
Jump Drive (6,000 unit range)
Invisibility to Tactical
Cloaking device (60 seconds)
Invisibility on Main Screen High-speed turning

Due to their ability to cloak, jump, or warp, Skaraan ships are often hired to attack USFP Deep Space Stations in the opening phases of an invasion.

From "Xenomorph Biology" by "Gryphon": (Some of this information may be speculation)

Skaraans are shorter and stockier than humans on average. To Terrans, they resemble the mythical centaur, with four legs, two short arms, an elongated head, and a long prehensile tail. They have thick, leathery reddish-brown to yellowish-brown skin and a wide strip of shaggy hair that extends down the back from the bridge of the nose to the base of the tail. They are famous for their adaptability, endurance, and shrewd dealings. They are infamous for their almost single-minded pursuit of profict at the expense of most other species' ethical or moral considerations. They are enthusiastic slavers and pillagers who are willing to undertake the destruction of entire populations if the return on investment is rapid and large enough, but as mercenaries they will readily switch sides mid-battle if the other side makes a better offer.

Skaraans are pseudo-marsupials whose male and female genders exist as a symbiotic pairing after the larger female accepts the much smaller, blind, hairless male as a mate. This pairing usually occurs very early in the development of juvenile Skaraans, and those juvenile males from fail to pair as a "primary" with a juvenile female within the first three or four years of life wither and perish unless they are accepted as a "secondary" by a mature female who has absorbed her original mate. The absorption of a "primary" and acceptance of a "secondary" is driven by metabolic shifts that are not well understood by Terran exobiologists, but the experience is known to be a deeply traumatic occurrence in a Skaraan symbiont's life, and much Skaraan literature and operatic drama centers on it. The Skaraan "pouch" is actually a mucous membrane chamber that houses the female's egg cilia as well as a secondary central nerve stem into which the male Skaraan inserts his tail.

Gradually, over a period of years, the male Skaraan's tissue fuses with the female's until his body, save for his sex organs, can no longer be distinguished from the wall of the pouch and his nervous systems combines with his mate's. The male preserves many conscious as well as autonomic functions that the female can clearly perceive. Skaraan creativity and treachery are sometimes attributed to their being literally "of two minds". The Skaraan symbiont's average lifespan is roughly half to two-thirds that of the average Terran.

Skaraans refuse to pay taxes to any government as a deeply-held principle, although they will make separate contracts to pay a percentage of carefully-defined net profits to a government in exchange for specified rights of operation for a limited period of time. They are the most open-minded towards other species as well as the most physically adaptable of all the major starfaring races. They can be found mingling and trading with other species in virtually every corner of the known galaxy, even when and where they are not welcome. Individual Skaraans rarely accept employment outside of their own species' War Corporations, finding other species' governmental regulations and business codes of ethics overly restrictive, but Skaraan corporations regularly employ the members of other species and trade representative.