Keriath the Shrouded - History: The Human colonists of the Totem System had long prided themselves on their independent spirit, and by the time they raised the alarm that they were under attack, the Chaos invasion led by the Tzeentchian Greater Daemon Keriath the Shrouded was already well advanced. The Exorcists were first to respond, and upon landing on the cardinal planet Totem IV, they were immediately beset by a huge host of Tzeentchian Warp-spawn. Though these eldritch horrors had the numbers to overwhelm the Astartes, the Exorcists' resilience of spirit was formidable even by the measure of Space Marines. Whether by some quirk of genetics or the invisible will of the Emperor Himself, they found themselves able to overcome the corrupting touch of sorcerers and Daemons in situations others would deem hopeless. So it was on Totem IV, as the Exorcists advanced boldly through the planet's blasted cityscapes, taking considerable physical damage but never yielding to the assaults their twisted foes made on their minds.Angered by the Exorcists' strange resistance to the mutagenic gifts of Tzeentch, Keriath the Shrouded sought out their leader -- Chapter Master Enoch Trismegistus -- and hurled his entire psychic essence into the stoic Space Marine's mind. Even the heightened resolve of the Exorcists was no defence against such a powerful entity, and the Chapter Master succumbed to the possession. Yet Keriath's victory was not complete; though the Daemon spoke through his host's mouth and did much damage to the Exorcists' position, internally Trismegistus battled on, fighting a desperate battle of wills against the Daemon and putting its own psychic defences to the test.While this ordeal took a grave toll on the Chapter Master's psyche, it gifted him with profound insights into the weaknesses of his daemonic foe and awoke a measure of his own latent psychic ability. In a feat of immense mental strength, he reached out to the mind of Chief Librarian Goetos, and together the two Exorcists drew out Keriath and banished him from realspace.The consequences of this episode were momentous for both Trismegistus and his Chapter. Unknown to the Exorcists, a Radical Inquisitorial sect known as the Plutonians had already developed suspicions concerning the Chapter's unusual spiritual resilience and hadembedded an informant in a menial position within the Chapter Command. When this spy reported on Trismegistus' daemonic possession, the Plutonians acted swiftly, asserting their authority as Ordo Malleus agents to relieve the Chapter Master of command and establish purpose-built quarters on the Chapter homeworld of Banish.Here Trismegistus was interrogated relentlessly. Only after many solar months was the Space Marine absolved and reinstated as master of his brethren. This was only the beginning, however. In the course of their interrogations, the Plutonians had laid out to Trismegistus their own Radical theories concerning daemonic possession and how its controlled use might be a paradoxical weapon in the war against Chaos. Perhaps they broke their silence out of vanity, expecting the Chapter Master to face the flames of oblivion soon enough. But Trismegistus had drunk of Keriath the Shrouded's vast intellect and realised the warped genius of the Inquisitors' plan. Once his purity had been proven beyond doubt, he made his own radical proposal to the Plutonians, pledging his incorruptible brethren as partners in their cause.Acting in utmost secrecy, the Plutonians therefore remained on Banish permanently to oversee a programme that would be met with outrage if known to the wider Imperium. Entering a forbidding facility known as the Halls of Tempering, each new Exorcists recruit -- and each compliant existing Astartes warrior -- would be subjected to daemonic possession like Trismegistus had been, albeit by entities of much lesser power and under tightly-controlled conditions. After a period of intense monitoring and scrutiny, the Inquisitors would then drive out the Daemon and return the victim to the care of the Chapter for a further phase of recovery and reflection. So began a unique Chapter initiation ritual that continues to this day.Those who successfully emerge from the ordeal bear disturbing physical and mental scars but also exhibit qualities that, in the Plutonians' view, justify the brutal ordeal. The process seems to render the Exorcists still more fearless and resilient to daemonic corruption, and it gifts each battle-brother with personal revelations of the nature of Daemonkind that serve them well in later clashes with the servants of the Ruinous Powers. Whatever the true extent of these changes, the Exorcists maintain a stony silence on all matters of Chapter training and tradition, knowing that even a single breach of secrecy could be their undoing.