The Nephilim are an insectoid race from the core of the known galaxy.
The emergence of the Nephilim was prophesied for millennia by the Kilrathi in the ancient prophecy known as Kn'thrak, which foretold the dawning of an era of "great darkness", when a race would come forth to destroy all who reside within the galaxy. This era would begin when "one who has the heart of a Kilrathi, but is not Kilrathi born" brought destruction upon the Kilrathi. This prophecy was one of the primary drives for the Kilrathi's deeply-rooted warrior culture, as they constantly fought to ensure their readiness when their prophesied enemy would arrive. If they were to fail in their pursuit of galactic conquest, their legendary enemy would come forth to destroy the Kilrathi and their foes, who in the eyes of the Kilrathi "star gods" were unworthy to know victory. To the Kilrathi, defeat at the hands of a lesser combatant would bring about dishonor unmatched by any other, and they would be condemned to destruction upon the coming of Kn'thrak.
In 2681, the Nephilim first emerged in the Kilrah system, encountering a Terran Confederation science team on the TCS Devereaux. In that engagement, the Nephilim destroyed the Devereaux, killing all who were on board, although not before they were able to send a distress signal. The Nephilim established a base of operations in the system from which to initiate a large-scale invasion of the known galaxy, within the heart of the former Kilrathi Empire.
In the year that followed, the Nephilim waged war against both the Kilrathi and the Terrans, conquering dozens of star systems and massacring countless victims as they swept across the frontier. Alarmed by the losses experienced by both sides in the conflict, the Terran Confederation launched an investigative action against this new threat, spearheaded by the newly-christened TCS Midway. This soon unfolded into what is now known as the Nephilim War, in which both the Terrans and the Kilrathi fought desperately to contain the Nephilim threat.