Aggressor Sentinel Eliminator
From Halopedia, the Halo wiki
During the Battle of Installation 05, these Sentinels were deployed to contain the Flood outbreak on the ring. Several of these Sentinels fought against Thel 'Vadamee and his forces on the installation.
Sentinel Eliminators only appear in-game in Halo 2 and its Anniversary remake, appearing on the levels Sacred Icon and Quarantine Zone as enemies for the player to fight against. Eliminators are given the more powerful Sentinel Eliminator beam and have a four second delay before their shields recharge and a one second recharge time, compared to the eight seconds delay and two second charge time of the Major. In-game, the Eliminators are given the "Captain" enemy flag.
Eliminators appear in Halo Infinite as prop assets on the multiplayer map Fragmentation - these Sentinels are destroyed and are merely a part of the map's background scenery, rather than an active part of the gameplay experience.
Sentinel Eliminators primarily appear in the campaign of Halo 2. Though they have never been named in any canonical capacity, the in-game files of Halo 2 refer to them as Eliminators. A common fan-misconception revolves around the use of the name "Sentinel Major" to describe these Sentinels; in actuality, the Major Sentinel is a different kind of enemy in addition to the Eliminators in Halo 2.
A lore stream conducted by 343 Industries writers Jeff Easterling and Kenneth Peters indicated that while the eliminators have been discussed internally, as of 2018 they had no particular designation for them and just considered them a different kind of Aggressor.