From Halopedia, the Halo wiki
Eradicators can function autonomously like Aggressor Sentinels, but are usually used as personal Combat skins for executor constructs in charge of Forerunner installations. A Monitor, Sub-Monitor, or some other Forerunner construct can dock within a cradle inside the Eradicator's central chassis and take control of the machine, using it to confront localized dangers directly. The Eradicator was manufactured by Ferrarius Assembler Vats.
The Eradicator has four offensive appendages that can be outfitted with a variety of hard light-based weaponry, usually shard projectors. In addition, it has a powerful sterilization beam that can be fired from its central unit. In the event of close quarters combat, the Eradicator can generate a damaging pulse that knocks enemies back. The Eradicator is also equipped with small reconstitution emitters, as well as energy shielding, and an impulse drive.
The Eradicator has two significant design flaws, the first being its lack of maneuverability and relative slow speed. Furthermore, if one of its offensive appendages is destroyed, the Eradicator will temporarily freeze up.
During the Battle for Zeta Halo, when John-117 and the Weapon attempted to shutdown the first Spire in order to halt the Reformation, they incurred the wrath of Adjutant Resolution, Zeta Halo's Sub-Monitor. Adjutant Resolution summoned an Eradicator, which he entered and assumed control of, and then proceeded to attack the Master Chief. The Chief managed to destroy the Eradicator, though Adjutant Resolution escaped unharmed.
Later, when John-117 stormed the Command Spire, Adjutant Resolution confronted the Spartan again, this time utilizing an improved Eradicator. Once again, the Master Chief destroyed the Eradicator, and once again, the Adjutant Resolution survived.
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