"It cannot be stopped, I've seen it myself! His ship- it's massive, larger then entire cities! It's hopeless! I've see the UNSC try to stop it - and their attempts just rippled it's shields! Nothing more!"
―A panicked civilian, on the Harbinger of Extinction.
The Harbinger of Extinction was the sole Durom-pattern OCS-class dreadnought that served as the flagship for Imperial AdmiralXytan 'Jar Wattinree. Once thought to be the largest warship ever constructed by the Covenant at the time of its discovery, the Harbinger was commissioned specifically to lead the campaign against the UNSC. Second only to the Hegemony's CSO-class supercarrier in terms of shielding and raw firepower, the Harbinger was unique in that it's main gun was recently reversed-engineered from a Forerunner artefact, unleashing unimaginable destruction on it's opponents.
Commissioned by the previous triad of Hierarchs, the Harbinger was assigned to lead the Fleet of Righteous Purpose during the early portion of the war. Responsible for the destruction of dozens of colonies and hundreds of warships, it would become the symbol of the Covenant's inevitable victory. It was with this ship that Xytan would earn the nickname of "World-Killer" among humanity, as he used it to personally reduce hundreds of population centres into melted glass. Entire fleets of warships would perish against it's might within a single battle, and it was often truthfully claimed that at no point did it's shields fall in battle during this period.
After Xytan's exile the Harbinger would be buried within the bowels of High Charity. Dozens of aspiring fleetmasters would attempt to requisition the dreadnought at their request, all which were refused by the High Prophets for various reasons. Only Thel 'Vadamee would receive their blessing, and he would deny it's use - while no friend of Xytan, he had enough respect to refuse the idea of using one of his rival's most potent tools. With no one else fit to succeed the Imperial Admiral, the Harbinger would sit silent for more then a decade. It was only during the Great Schism that the warship would return to the battlefield, trading hands dozens of times until it vanished during the Battle of Sigmus III.
The immense warship that would become the Harbinger was always destined to be a legendary weapon, as the very foundations were designed by the highly respected Firuan brothers of the Lathe of the Enlightened, located on Song of Victory. A centuries-old guild of some of the most talented architects in the Covenant, the Lathe had prided itself on the construction of master-crafted warships for the most influential of fleetmasters. As a result of this reputation, this organisation had a history of being approached by the High Prophets to design many of their unique flagships, and it is this record that drew the newly-promoted Imperial Admiral of the Covenant Xytan 'Jar Wattinree to them.