I was hoping by now that someone would have drawn some attention to this sinsiter and mysterious figure... if someone has, my searchfu is weak and turned up nothing.

Cassilda Cognos first came to my attention because of her peculiar name and the connection it has with the King in Yellow. However, I quickly began to see her name pop up other places. The major interest is her connection with the Tyrant Star and the formation of the Tyranite Cabal.

1. Acording to the Rulebook, Lord Sector Hax, Chief Astropath Xiao and a few others even know of its existance. Head of the Tyranite Cabal is Lord Inquisitor Zerbe. Calixian High Lord Inquisitor Caidin personally appointed Zerbe to head up this cabal. At this point Cassilda Cognos has not been mentioned.

2. In the Inquisitor's Handbook under the Tyrantine Shadow Agent, we get a glimps of her machinons behind the sceens. Within the Tyranite Cabal is another deeper organization the Tenebrae Collegium, set up by none other than Cassilda Cognos. The fluff text at the bottom of the page tells us that she was one of Zerbe's most trusted confidants as well as she personally had much to do with swaying Caidin to create the Tyranite Cabal and Tenebrae Collegium in the first place. This would lead me to think she is extremely politically powerful in her own right, having the ear and swaying two of the most important Lord Inquisitors in the sector?

3. She is supposedly dead

“Lest the truth devour all.”

— Memento Mori on the Tomb of Inquisitor Cassilda Cognos.

4. In the radical's Handbook under the Blighted Schola, she agains finds mention. The Blighted Schola was founded by the Golgenna Coven who included but certainly not limited to: four inquisitors, Simion, Nihul, Estarz and Alhain. Prefect Maximus of Scintillia Olius Lupus and Admiral Gornian Sans. It was noted that the Inquisitors were all close associates or pupils of Cassilda Cognos. Again, this could not be a coincidence. She is shown to be a very shadowy power behind the throne sort of figure. The Schola was purged by Puritan Inquisitors... but many escaped to work for Radical Inquisitors... this suggests that Cassilda Cognos is most likely a Radical, and it is quite posible that Zebre is sympathetic to the Radicals if not actually secretly one himself. Also because of the high levels of the civilians, and the connection between Cassilda, Zebre, Caidin and Hax that in fact the conspiracy reaches all the way to the top!

5. Last I'd like to point out Lady Olianthe Rathbone is believed to be one of Zebre's old Interrogators. She is also a Radical. They appear to have no relationship however, though that could just be because she is cold and aloof. I highly suspect she is also part of the overall conspiracy.

Myself I have ideas and beliefs, but would like to hear what others think of this emmatic figure

and any other information they have come across that links her to the powers that be and the further mysery of the Tyrant Star.

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4. In the radical's Handbook under the Blighted Schola, [...]

IIRC she is also mentioned under Tenebrae Collegium in the chapter about minor radical factions as well as in a short blurb at the start of the book, where Inquisitor Herrod visits her tomb or something (not sure...)...

You are correct Luthor, RH pg 125. The passage details her motivatins more clearly for creating the Tenebrae Collegium. It also suggests that Caidin "alows" the continued existance of the Tyranite Cabal, which seems to be at odds with his attitude twords something he had a hand in creating according to the description in the Rule Book. It also furth suggest that Cassilda may have knonw more about the Tyrant Stars secrets then she may have ever told anyone, which is why she was more ferverant that Zebre about it. Its saying quite a lot when you create an organization withnt your secret organization to kill members of your parent organization when the time comes to do whatever it is you set out to do...

I also found the reference to Inquisitor Herrod in Cassilda's tomb. It starts in the table of contents of Deciples of the Dark Gods.

I have my suspicions she's not actually dead, at least not in the truest sense.

There is also the fact that the villain Ferran Ghast (detailed in DotDG and Ascencion) is said to have been a personal pupil of Cassilda Cognos before he betrayed the Holy Ordos.