The Grey Rebellion was an insurrectionist movement which occurred approximately five hundred and fifty years before the beginning of the Human-Covenant War and was headed by former Fleet Master Kyrin 'Forus. The Rebellion was significant enough in the Covenant Empire to usher in the 29th Age of Conflict due to the entirety of the 2nd Fleet of Undying Justice, under the command of Kyrin 'Forus, breaking off from the Covenant as a whole and becoming an independent entity. This schism was signified by the removal of rank colours and ornaments, where the name Grey Rebellion originated from.