Reclaimer

A "Reclaimer" (Latin: Homo Sapiens Augeous) is an individual who, whether by chance or by precedent, has been placed in charge of retrieving an item known as the Index, returning it to, and subsequently placing it into a control panel within a control center on a Halo structure to activate a massive superweapon. The word is first used as a title bestowed upon a Staff Sergeant Marvin Mobuto in Halo: The Flood and Master Chief in Halo: Combat Evolved by an artificial intelligence construct, designated 343 Guilty Spark by its creators, the Forerunners. Also "Augeous" is Latin for augmented, so it is possible the Forerunners were basically human but stronger, smarter and faster or in one one word better. This could also be refering to the fact that the Master Chief, the most recent reclaimer, is physically augmented.

History
The only known role of a Reclaimer is to recover the "Index" and return it to the Halo control center or Ark Control Center. Doing this would activate Halo's ability to destroy all sentient life within twenty-five thousand light years, and would also activate other Halos, causing the entire galaxy to be purged of sentient life. This would be done to prevent the spread of The Flood, which can only be accomplished by destroying all sentient life with a biomass sufficient enough to sustain them. This would then destroy the Flood via starvation.

343 Guilty Spark assumed, for unknown reasons, that the human soldier Master Chief was a Reclaimer and also that The Arbiter was a "Meddler" in Halo 3. However, Commander Keyes and Sergeant Johnson were also called Reclaimers by 343 Guilty Spark. 2401 Penitent Tangent also refers to Master Chief as a Reclaimer, implying that all Monitors recognize him as such. In addition, in Halo: The Flood the Master Chief encounters the corpse of Sergeant Marvin Mobuto in the Library, whom Spark also refers to as a Reclaimer.

It is very likely that all humans are Reclaimers, supported by comments made by 343 Guilty Spark. As the "successors" of the Forerunners, it would be their task to activate the Halo Installations, a task that Covenant species are incapable of accomplishing.

It is also likely that 343 Guilty Spark does not recognize Reclaimers as separate beings. When talking with Master Chief in Installation 04's Control Room, he says, "Last time, you asked me, would I do it? Having had considerable time to ponder your query, my answer has not changed." It seems that Guilty Spark was referring to a question posed to him by a Forerunner prior to the activation of Installation 04 100,000 years ago.