Abaddon

"He now realized that it was a Precursor's version of an ancilla-one as far beyond those of the Forerunners as a keyship was to a wooden raft."

- IsoDidact on Abaddon

Abaddon was a powerful Precursor construct later mythologized by the Forerunners as the Organon, a rumored Precursor artifact of incredible power, believed by some Forerunners to be able to activate all Precursor artifacts. It was considered to be the most sought-after Precursor artifact by Forerunner archaeologists.

Several years prior to 97,445 BCE, Bornstellar Makes Eternal Lasting sought the Organon on both Edom and Erde-Tyrene using a pair of human guides to lead him to its presumed resting place in the Djamonkin Crater. Instead he found the Cryptum of the Didact, who stated that the Organon did not exist, at least not in the form imagined by most Forerunners.

At the close of the Forerunner-Flood war, just minutes prior to the firing of the Halo Array, the Gravemind told the Librarian that the Organon was actually the Domain, a metaphysical information storage medium created by the Precursors and embedded within their ancient structures. Its takeover by the Flood in the last years of the Forerunner-Flood war allowed them to use Precursor artifacts as weapons, and so gain an edge over the Forerunners. When the Halo Array was fired, the Domain and all knowledge within would be lost forever, along with all Precursor artifacts.

Over a century later, during the surviving Forerunners' mission to Maethrillian after the reintroduction, the IsoDidact and his party discovered that the "Organon" was in fact a Precursor artificial intelligence named Abaddon, who helped ancient Forerunners first access the Domain after the Forerunners wiped out the Precursors. Abaddon had been buried and sealed deep within the capital world and now sought to bring the surviving Forerunners to trial for their crimes.

List of appearances

 * Halo: Cryptum
 * Halo: Silentium
 * Halo 5: Guardians
 * Halo: Fractures
 * Promises to Keep