Not every Custodian kept his vigil within the Palace walls. The Emissaries Imperatus were those of the Legio sent out into the wider Imperium as the Master of Mankind's personal envoys, His eyes and His verdict made flesh. Where a matter was too grave for the Administratum and too delicate for a Legion, a single Custodian might be sent to observe, to counsel, and — if the need arose — to kill. Their word carried the Emperor's own weight, and few, even among primarchs, cared to defy an Emissary to his face.
During the Heresy their burden grew heavier still. As loyalty fractured and truth grew murky, the Emissaries Imperatus were dispatched to sever the faithful from the traitor, to salvage what could be salvaged, and to render judgements no other authority could carry. They walked alone into warzones the primarchs could not reach, bearing the Emperor's trust into the darkest corners of the war. Many did not return; those who did brought back knowledge that shaped the Legio's grim understanding of just how far the rot had spread. To be marked for such a duty was among the highest honours the Legio could bestow, and among the loneliest, for an Emissary walked apart from his brothers and answered to the Emperor alone.
Legio Custodes
Order of battle
The The Emissaries Imperatus field the units of the Legio Custodes — a detachment from the roster:
Kindred formations
Other Legio Custodes formations
The Aquilon CohortThe Aquilon Cohort gathered the Legio's Terminator-armoured shock warriors, Custodians whose engineered frames alone could bear the cumbersome Aquilon plate into the direst breaching assaults.
The HykanatoiThe shield-companies of the Hykanatoi formed the standing guardian host of the Palace, the disciplined core of Custodians who held Terra's inner precincts through every hour of the Great Crusade and the Heresy alike.