- "Blackest of Ages, Saddest of Times. Let none give name to he that laid us low..."
- — The Chant of Days, Scrivener Obyss Mak
The Age of Apostasy was a second period of civil war in the Imperium of Man during the early 36th Millennium when the Imperium's government was essentially seized by a single man, High Lord Goge Vandire, who ruled the Imperium according to his own wishes instead of in accord with the Emperor's will. High Lord Vandire was in power for almost a standard century before being overthrown and slain by his own bodyguards, the Daughters of the Emperor, who later became the Adepta Sororitas. Vandire was replaced as the Imperial Ecclesiarch by Sebastian Thor, who unleashed the Imperium's second major era of reform. The Age of Apostasy is considered to be one of the bloodiest eras in the Imperium's history after the terrible civil war of the Horus Heresy.
The single most powerful unifying force in the Imperium of Man is faith: the reverent worship of the God-Emperor that binds loyal Imperial citizens together. But this faith is manipulated all too often by the power-hungry and the over-zealous. Thus it was in the early centuries of the 36th Millennium with the insane tyrant High Lord Goge Vandire, who managed to become both the Imperial Ecclesiarch, the high priest of the Adeptus Ministorum and High Lord of the Administratum at the same time. With his control over both the priesthood and the primary bureaucracy of the Imperium, Vandire was easily able to utilize bribery, blackmail, coercion and murder to cement his power base among the other High Lords of Terra, becoming the first among equals. The result was the Reign of Blood and countless other wars of faith, all fought to maintain Vandire's iron grip upon the Imperium. Countless billions died in the resulting strife and the Age of Apostasy became the bloodiest period in Imperial history since the Horus Heresy five millennia earlier.
The Reign of Blood lasted for seven decades before a messenger delivered the news to High Lord Vandire that heralded the end of his tyranny. On the world of Dimmamar a man named Sebastian Thor and his sect, the Confederation of Light, denounced Vandire as a traitor to the Emperor and resurrected the rites and rituals of Emperor-worship and the Imperial Cult that had been outlawed by Vandire. They spoke of hope and an end to Vandire's bloody rule, and the people who had suffered greatly under the tyrant flocked to Thor's banner. As star system after star system joined the Thorian movement, Vandire tried to stop them and sent a military force to crush them, but it was lost in a sudden Warp storm. By that time the rebellion had spread across much of the Imperium.
Vandire's fate was finally sealed when the Adeptus Mechanicus of Mars and the Adeptus Astartes, who had remained uneasily neutral in the conflict, finally threw their efforts into deposing the corrupt tyrant on Terra. Several regiments of Mechanicus Skitarii ('Tech Guard') and a number of Space Marine Chapters assaulted the Ecclesiarchal Palace but the formidable fortifications of the Palace, combined with Vandire's own elite female warriors, the Daughters of the Emperor (which Vandire renamed the Brides of the Emperor), ensured that the assault swiftly bogged down into a long siege.
In the end, it was the intervention of the Adeptus Custodes, the Emperor's personal guard, that tipped the scales. Previously isolated from the outside world in the Imperial Palace, these doughty warriors learned of the war raging and added their weight to the siege. It was a member of the Custodes who showed the Daughters of the Emperor the heresy they had been unwittingly involved in, and their enraged leader Alicia Domenica swiftly delivered the coup de grace to Vandire. After hearing Domenica pronounce sentence upon him, Vandire's last words were reported as "I don't have time to die...I'm too busy!"
With Vandire's death, the Mechanicum led the Imperium in a bloody purge of his loyalists. Sebastian Thor was tried for treason, acquitted, and eventually became the new Ecclesiarch. The Thorian reforms ensured that the Imperial Cult's priesthood would never again be in a position to control the Imperium as thoroughly as Vandire did.
One notable result of the Age of Apostasy was the founding of the Adepta Sororitas, or Sisters of Battle, an all-female army that was the sole military force permitted to the control of the Ecclesiarchy. This organisation, which emerged from the Brides of the Emperor, became one of the Imperium's primary agents in keeping its internal enemies in check, devoting their efforts to combating, amongst others, rebellious worlds & governors, heretics, mutants and rogue psykers. The Sisters ultimately became the Chamber Militant of the Ordo Hereticus, the arm of the Imperial Inquisition tasked with hunting down internal threats to the Imperium that was created in the wake of the Age of Apostasy.
- Warhammer 40,000 Rulebook (6th Edition), pg.167
- Warhammer 40,000 Rulebook (5th Edition), pg. 122
- Codex: Sisters of Battle (2nd Edition)
- The Outcast Dead (Novel) by Graham McNeill
- Mechanicum (Novel) by Graham McNeill