Others

The "Others" are or were a major Ulterior civilization known to the Covenant. Located in a spiral arm on the opposite side of the Milky Way galaxy from the heartlands of the Holy Ecumene, possibly in the Norma and/or Scutum-Centaurus arms, The Others are described in ancient travelogues as a formidable power and thriving empire, though some of the details documented in said travelogues are peculiar and may be exaggerated. The civilization's very existence is only inferred from scattered mentions in ancient Covenant records, and even their real name remains unknown; the Covenant evidently called them "Others" because the two civilizations were (or were seen as) roughly equal in influence within the galaxy. The two civilizations evidently had sporadic contact with one another up until around eight centuries before the Great Schism, though no consistent relations were ever established.

Roughly four centuries before the Great Schism, a Covenant remote outpost in the Perseus Arm roughly 30,000 light-years spinward of the heartlands of the Holy Ecumene observed anomalous and widespread energy signatures propagating through slipspace, seemingly originating from the far side of the galaxy. While the Covenant could not parse the energy signatures' exact exact nature or origin, it was hypothesized that they may have been the result of mass-scale slipspace transit, or mass-scale weapons deployment between two civilizations. The Ministry of Vigilance sent scout ships to investigate, though none returned and no subsequent missions were attempted. It is evident that the opposite side of the galaxy was one of the regions the Covenant generally avoided traversing even as they embarked on their grand artifact-hunting expeditions, which may hint that the Covenant feared to intrude on the territory of a technological peer or superior civilization in those regions.