From Halopedia, the Halo wiki
Prior to joining Atriox and the Banished, Teranus served the Covenant. He traveled aboard the Enduring Conviction to Installation 00, arriving on November 25, 2558. He took great delight in viewing the slaughter of the humans at the Henry Lamb Research Outpost. On December 7, he recorded a log for his captain, in which he expressed his frustration with the Sangheili aboard the Enduring Conviction and decided to find some Unggoy to beat for sport.
Personality and Traits
Teranus holds the Sangheili in the Banished with disdain due what he perceives as pompousness. He does not trust them, largely because they declined an invitation to celebrate the massacre of the humans on the Ark. During said massacre, many Unggoy were killed by friendly fire, but Teranus held this as wholly inconsequential. To him, Unggoy are of no real value and he even enjoys beating them for sport. The suffix, "us", at the end of his name signifies maturity or experience in battle.
List of appearances