An ONI-produced illustration based on eyewitness accounts of a then-unknown Covenant enemy encountered by UNSC forces on Paris IV in 2549. Categorized at the time as a "special purpose sniper" based on its role, the species has since been identified as an Ior.

The Ior are a sapient species inhabiting the moon of Tauwen, located near the California Nebula.

They were discovered by the Covenant around the 21st Age of Discovery (c. 2120s). At the time of their discovery, the Ior were in a preindustrial state and had a small population of only around three million individuals. It quickly became apparent that the Ior are not native to Tauwen, though they have inhabited the world for what must be thousands, perhaps tens of thousands, of years. Study of the Ior's cultural myths as well as artifacts and ruins found on Tauwen has led Covenant scholars to speculate that the Ior may be a forgotten colony of a more widespread spacefaring species, with the Jehioi being the most likely option due to various apparent commonalities between the species. Since their discovery, the Ior have been part of the Covenant fringe, though there were plans to eventually integrate them to the hegemony proper. To deter pirate and raider incursions to the moon, the Covenant established a monastery-fortress on Tauwen, through which the local monastics have sought to educate and "civilize" the Ior population. As such, a number of Ior have been able to become part of the wider Covenant society. The Covenant and its member organizations occasionally employed these Ior as assassins and snipers, though they were not formally integrated to the ministerial hierarchy.

The Ior are an arboreal species known for their thin, lithe bodies and unusual monoped body structure. They possess three long limbs with three dexterous digits per limb. While their sole lower limb is technically the Ior's only "leg", all of the limbs are relatively multipurpose and can be used as either arms or legs depending on the situation. As an arboreal species, the Ior are at their least comfortable on land where they move either with an odd hopping motion or walk on all of their three limbs. In vertical spaces such as trees, however, they thrive, nimbly using all their limbs tow swing themselves from one branch to another. Due to this, they also have an excellent spatial awareness, reflexes and sense of orientation. Due to their arboreal nature and low-gravity habitat, the Ior also adapt to space travel rather easily. They are relatively small in stature, standing at around 150-170 centimeters tall.

Cognitively, they fall in the Congruent side of the Congruent-Enigmatic scale despite their peculiar body plan. The Ior natively organize their society into tribes and tribal confederacies, with relatively developed customs and languages. When educated, they are capable of grasping much of the Covenant's culture, religion and society. However, their ability to speak Pan Sangheili is somewhat limited by their vocal chords, which are most at home producing various forms of clicks and whistles.