The Skrel are a mysterious alien race from an unknown world that periodically attempts to drive humanity off Nova Prime which they effectively consider a sort of holy land. No human has ever laid eyes upon the Skrel, and their true name (if they have any at all) is unknown to humanity.
No Skrel has ever been seen or studied by humanity, but observations of the Ursa and their ships has led the Savant to believe that the skrel themselves may lack optical organs, seeing the world in some unfathomable manner.
Most of what is known about Skrel technology is known from the examining of their spacecraft and robotic drones. Their ships are made from alloys that had never been encountered by humanity until after the Skrel attacks (causing speculation on how far the Skrel had traveled), and they are equipped with energy shields highly resistant to fusion-burst weaponry.
It is known that their technology is entirely different from the race that unwittingly provided humanity with lightstream travel, but they seem to have very efficient interstellar spacecraft that have been able to avoid much of humanity's satellite networks. When the Skrel returned unexpectedly in 933 A.E., it was noticed that their designs had changed little since their original invasions.
They have also demonstrated significant abilities with genetic engineering with the creation and continued development of the Ursa, a powerful creature that has proven highly effective against humanity.
When humanity left earth they had no knowledge of the Skrel, the first attack came as a terrible surprise in 243 A.E. when a Skrel fleet arrived in the skies over Nova Prime City. Despite steep odds the Rangers defended the populace and the alien threat was routed. Little Skrel technology survived the battle, robbing scientists of a chance to thoroughly study the enemy. The United Ranger Corps relied entirely on fusion-burst cannons for defense, but they proved ineffective against the Skrel Hulls.
That devastating days-long attack confounded the Rangers, commanded at the time by Patrick Wulf. The troops braced themselves for a ground assault to follow the airstrikes, but it never came. In the end, not a single Skrel vessel intentionally landed on the surface.
Instead, the Skrel bombarded Nova Prime City and the outlying colonies with a soul-crushing death toll. What baffled the tactical experts was how selective the shots were, attacking the man-made structures and almost reverently leaving the world itself untouched. That alone saved countless lives.
The Rangers were stymied and the people were panicking. The Primus, M'Liss Cornetta, told the worshipers seeking answers, "we have strayed, my friends. We have strayed from the precepts our people have long embraced. And this is the result. Death. Destruction. the pain of knowing our loved ones are lost to us. But remember-this is not the first time we have been tested. Our Ancestors took off from Earth with nothing but the unknown ahead of them. Despite everything, they survived. And we will survive as well-by finding the strength our ancestors discovered on the arks. We have grown complacent, my friends. We allowed ourselves to believe that we have conquered every challenge-that we were the masters of our house. But there is always someone greater."
While the Primus saw it as some form of cosmic punishment, the Prime Commander wondered if the planet held some strategic importance, implying other life lurked among the stars and posed new unimaginable threats for the people. Savant Bree Kincaid conjectured the technology on display didn't match that of the alien race that accidentally bequethed Lightstream technology to humans, but she saw the attack patterns showing an almost reverent desire to leave the world's ecosystem untainted.
During those dark times, Carter Raige was convinced he saw a skrel vessel crash, and his father, [[Jason Raige,, led combat flyers in search of the wreckage, hoping to find clues as to the enemy's appearance, intentions, or technology. While the flyers found nary a piece of shrapnel, Carter Raige went deep within a cevasse where he soon found the ship. What he discovered of the flying craft was badly burned, while its crew had been incinerated, depriving the Savant Kincaid of alien corpses to study. Carter Rage, though, found intact pulsing modules that he took from the ship and brought back to the Savant.
These modules turned out to be energy-field generators that were capable of blocking up to 80 percent of fusion-burst cannon fire. Additionally, studies showed the fields also interfered with the Rangers flyers' sensors which explained why the aircraft never located the wreckage. When studies showed t fusion-burst cannons would remain ineffective against the Skrel, Savant Kincaid accepted her cousin Jack Kincaids recommendations, and that turned the tide. As soon as the quantum-trapping weapons were deployed, the Skrel were speedily shot down. Within a day, the remaining Skrel ships withdrew from Nova Prime airspace and vanished.
The alien energy modules served as a warning that humanity now had an enemy with unknown motivation and superior technology. Preparation became the new watchword for the united Range Corps. Starting with Savant Bree Kincaid and her successors, efforts were made to begin salting the planetary system with satellites that would act as early warning beacons.
Resources were diverted to study the Skrel's approach and retreat, trying to determine where in the galaxy they had come from, which might suggest their motivation for attack. Additional concerns were raised over whether or not other races were out there and which ones might also harbor designs on Nova Prime or humanity.
Jason Raige, who succeeded Wulf as Prime Commander reconfigured the United Ranger Corps, creating an Elite response Squad that would be prepared to defend humankind should the Skrel return. Additionally, Response and Recovery squads were created to deploy wherever the Skrel Attacked. Based on their study from the initial attacks, unscheduled drills occurred with brutal regularity until Raige was satisfied the people would be protected.
It was not until 350 A.E. that the Skrel returned. The attack was brief but destructive. What turned out to be robotic drone craft arrived, fired, and self-immolated. There was still significant loss of life, including that of Prime Commander Esteban O'hara. How the Skrel eluded the satellite system was a concern, and in the aftermath Savant Tak Kawasaki insisted the entire fleet of satellites be upgraded, or replaced in addition to doubling their number.
Additional studies during the years following this brief attack yielded nothing concrete about the Skrel. They had clearly not been idle, though, as they did return bringing the Ursa with them.
Ever since that first infiltration of Ursa in 576 A.E. the Skrel have avoided direct attacks on Nova Prime until an unexpected and particularly brutal attack in early tenth century A.E. Nothin about the assault matched the few previous events, confounding military strategists. It was repelled but not before a wide swath of destruction befell the major cities on Nova Prime.
The goals of the Skrel are uncertain, there is no information concerning where they hail from, and no human being has ever seen a Skrel. The only thing that is clear is that they want humankind eradicated from Nova Prime and the reason why remains a hotly debated point of contention.
The mystery of their intentions toward Nova Prime is only magnified by the fact that there is no trace that the world has ever housed any intelligent life (or even significant complex life). Over many centuries geologists sought in vain to find evidence that there was ever civilization on the world.
The Skrel's long-standing enmity toward humanity remains the subject of academic speculation and has spawned countless works of fiction about who they are and what they desire.
It is unknown if the Skrel have a true name for their species, the term "Skrel" was coined by Carter Raige ancestor of Cypher Raige who, like his descendant, would grow to become a Prime Commander. He was in the canyons beyond Nova Prime City when the ships arrived, he was the first to be close enough to the alien ships to see the alien characters on their sides, calling them Skrel based on the characters similarity to English ones.