Nephilim

The Nephilim are an insectoid race that originally appeared in the Wing Commander universe.

History
While no definitive history of their existence exists among the various races of the galaxy prior to the Earth year 2416, 328 years after the Earth's destruction, it is believed that the Nephilim are natives of an empire near the galactic core. The only race who knew of the Nephilim's existence were the Kilrathi, who had predicted their arrival in the known galaxy for centuries preceding their war on humanity. Thousands of years before, Sivar, the Kilrathi God of War, had appeared to the first Priestess of Kilrah and he set in motion a prophecy that would predict the doom that would rain down on the galaxy:

''There shall come a time when one who has the heart of a Kilrathi, but is not Kilrathi born, shall rain cleansing fire down upon us. And Kn'thrak, a time of great darkness, shall embrace us''.

''Death itself shall pour forth, obscuring the stars in a veil of darkness. Theirs is the claw that tears flesh from bone.''

Theirs is the poisoned fang.

''Their numbers shall rend the universe barren and crush the breath from our clans. We shall be bathed in our own blood and rotted flesh shall be our fare. With a deafening thunder shall the dark age begin.''
 * -The Tome of Sivar

Kn'thrak
During the year 2416, Kn'thrak made itself apparent to the inhabitants of the galaxy. As Lina, Doon and Poppy emerged on the surface of the Earth, an alien wormhole emerged and a massive warship entered the system. The alien vessel fired upon the surface, killing all.

Soon enough, dozens of mysterious warships entered the Sol system through the wormhole, destroying Earth and setting the stages for an invasion of the galaxy.

Within the following weeks, several Kilrathi colonies, warships and space stations were destroyed by the Nephilim, as well as the majority of the ships sent by various alien races to investigate the attacks. Virtually no one survived these attacks, so both sides remained mystified as to what these attackers were and what they planned, so the Kilrathi and the alien races form the alliance to counter the Nephilim threat.