- "You believe that the wall separating civlilisation from barbarism is as solid as steel, but it is not. I tell you the division is a thread, a sheet of glass. A touch here, a push there, and you bring back the reign of pagan superstition, fear of the dark and the worship of fell beings in echoing fanes."
- — Primary Iterator Kyril Sindermann
The most famous and perhaps skilled of the Imperium of Man's Iterators during the Great Crusade was Primary Iterator Kyril Sindermann, who served as the chief Iterator for the Warmaster Horus' 63rd Expeditionary Fleet and dwelled aboard his great flagship, the Vengeful Spirit. Sindermann was a particular favorite of Captain Garviel Loken of the Luna Wolves, with whom he often discussed the weightier matters of philosophy and the reasons why the Emperor had undertaken the Great Crusade to force other human cultures into his Imperium, by diplomacy if possible, but by force if necessary. Sindermann was a dedicated atheist and powerful proponent of the Imperial Truth until the day during the Luna Wolves' conquest of the world designated Sixty-Three-Nineteen when he and several Remembrancers from the 63rd Expedition witnessed the daemonic possession of the Luna Wolves Battle-Brother Xayver Jubal. To see what could only be described as a daemon called every one of Sindermann's most cherished beliefs into question. He spent months after the incident cooped up in the Vengeful Spirit 's Archive Chambers hunting for answers in the knowledge of the human past. He was particularly concerned by one burning question: why would the Emperor have promulgated the atheistic doctrine of the Imperial Truth if he, as humanity's greatest psyker, was keenly aware that such entities existed within the Immaterium?
Sindermann eventually spoke with Euphrati Keeler, the Remembrancer who had taken hololiths and images of Jubal's hideous transformation, but had come to grips with her own confrontation with the daemonic by becoming a devoted follower of the Lectitio Divinitatus, the growing Imperial religious cult that believed in the divinity of the Emperor and ultimately laid the foundation for the Imperial Cult and the Ecclesiarchy. Sindermann attempted to use fragments of text and images taken by Keeler and other Remembrancers to decipher the religious text sacred to the Word Bearers Legion known as the Book of Lorgar which supposedly held the collected wisdom of many dark priesthoods and superstitious faiths across the galaxy and had been created after the Primarch Lorgar had completed his infamous Pilgrimage decades before. While reading a portion of the text aloud from the heretical tome, Sindermann inadvertently summoned a Lesser Daemon from the Warp that began to damage the library stacks of the Archives aboard the Vengeful Spirit until Euphrati Keeler banished the creature back to the Immaterium through the exercise of her extraordinary faith in the Emperor, after which she fell into a coma-like state.
This latest encounter with the daemonic broke Sindermann's remaining tenuous belief in the atheism and materialism of the Imperial Truth and forced him to confront the reality that he lived in a universe where spiritual beings did exist and could hunger for the lives and souls of human beings. In such a universe, the only thing that could protect men was the power of other supernatural beings. Thus Sindermann came to exchange the Imperial Truth for a new faith in the divine Emperor as embodied in the teachings of the Lectitio Divinitatus. By this time, the corruption of Chaos had wormed its way deep into the Warmaster Horus and most of his renamed Sons of Horus Legion, and so with the aid of Captain Iacton Qruze of that Legion, Sindermann, the Remembrancer Mersadie Oliton and Euphrati Keeler managed to escape the Venegeful Spirit during the start of the Battle of Istvaan III. They made their way to the Imperial frigate Eisenstein. They were taken in by the Death Guard Loyalists under the command of Battle Captain Nathaniel Garro and escaped from the Istvaan System to Terra after many trials and tribulations to warn the Emperor of his son Horus' great betrayal.
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