As the title implies, I figured I would compile all knowledge that we have of the emergent organizations. A more detailed post will follow, as I have to go. Needless to say, I will be focusing on the origins of what we know of as the Inquisition, including such characters as Iacton, Garro, and Kendel etc.
(Eek, double post! Don't smite me, please!)
What we know of Garro is that he, Iacton, and Kendel as told by Malcador in his speech "men of an inquisitive nature..." and "hunters who might seek the witch, the traitor, the mutant, the xenos..." is that they would become members (probably) of the Inquisition. We can assume from this that Garro and Iacton will probably BEFORE Horus is killed, train on how to fight Daemons. AFTER Horus is killed, it seems likely that Garro becomes some sort of Daemonhunter. However, what we do not know is whether this is as an Inquisitor, as a Gray Knight, or as a normal Astartes wearing his old Legion colors. If Garro does become a Gray Knight, that means that he has dormant psyker powers as all Gray Knights are psykers. However, if he remains an Astartes fighting in his old colors, he could be killed on sight by other Astartes. If, by chance, Garro does not become a Gray Knight, or continue to fight in his Legion colors, but becomes an Inquisitor, he would become the head of the Ordo Malleus. This seems likely as either he, or Iacton would be the head of the Ordo Malleus. Of course, for all we know, Garro is merely an Inquisitor, and some, as of yet, unnamed figure steps out and becomes the head of the Ordo Malleus. Perhaps Garro and Iacton, plus the seventy Death Guard, (And any who survive Istvaan III) could become the precursor to the Gray Knights. When the Gray Knights are unleashed and revealed, they may become either honorary members, or perhaps they become Garro's private army if he is elevated to Inquisitor. ANother possibility entirely is that Garro becomes an Alien Hunter. Though unlikely, it would make an interesting twist, as we can almost safely say that Garro becomes a Daemonhunter after the Flight of the Eisenstein
All of these are theories, mind you, and as such, we do not know which is true canon, but in any of these situations, you have nearly endless possibilities for some very interesting fiction and army background.
I have a surprise to follow....
Questions, Comments, Criticisms etc. are welcome.