The Casophilians are a subfaction within the Inquisition which consist of members that follow the Thorians' philosophy. The origins of this philosophy are traced to Saint Casophili who was a missionary in the Missionarus Galaxia during the early part of the 41st Millennium.
The teachings of Casophili involved the spread of the word of the Ecclesiarchy to the worlds in the southern part of the Segmentum Pacificus. On the planet Alena Three, the mission encountered minions of the Chaos Gods at the heard of several of the feral societies of that world. Using what few resources were available, Saint Casophili did what he could in order to counter the threat posed by the endemic and laid down the groundwork for a full Ecclesiarchy task force which was to continue his work. However, as their forces moved from one settlement to another where they preached the word of the God-Emperor, their foes began to take notice. The council of priests could no longer bear a further threat to their power which they used to rule the world and thus moved against Saint Casophili by capturing and torturing him in order for him to recant his errant beliefs.
According to the chronicles of Casophili, it is said that his arduous odreal at the hands of the twisted priests led to his death by the wounds he had sustained. Whilst it is recorded that he had died at the hands of his tormentors, a miracle happened five days later when the missionary's body was to be burnt on a sacrificial pyre to the Dark Gods. As the flames took hold on his body, Saint Casophili seemingly roused himself and jumped from the fires. Confronting his tormentors, he gathered a crowd and the story of the saint's resurrection spread quickly whereupon he led the people of Alena Three against their priesthood.
This occurrence would normally have attracted the attention of Resurrectionist Inquisitors but this faction only dedicate themselves to one aspect of Saint Casophili's tale. According to Casophili's written works in latter days, during the five days he was between death and resurrection, he said he was a bodiless floating sensation that was adrift in a sea of sound and colour. He also claimed that he heard a myriad of voices whispering whilst other bellowed that swirled around him. Furthermore, he spoke of a great light that suffused everything which he believed was the Emperor. The fact that the saint's soul returned to his body is not a concern for this Inquisitorial faction, as all Thorians believe that psychic energy can pass from an individual to the Warp and back again. However, it is the fact that Casophili's writings claim that there exists a place where the soul resides which dominates the viewpoints of the Casophilians.
The Casophilians know that Daemonic entities can pass the barriers between the Warp and the mortal world. They thus dedicate their studies to the transition of a Human soul from this world to the next. This makes them profound experts in the arts of Daemonology with a special regard to ritual summoning rather than incidental or malicious possession. These actions aim to find the means and knowledge to bring back a deceased man or woman's soul to the mortal world. If these actions are successful, than it would be the first step in bringing back the soul of the Emperor into a suitable mortal form. Further aspects that differentiate the Casophilians from other Resurrectionist beliefs is the fact that they openly embrace new ideas on their theories and thus work closely with Inquisitors of other learnings which prevents them from adopting a general, isolated view on their studies. This allows them to learn much from their interactions with other branches of the Inquisition and allows them to gain much from their experiences. Amongst the different philosophies, the Casophilians are often known to work in conjunction with members of the Anomolian Beholders as both fields of study work on the soul; one of the living and the other of the dead.