Liadova

Governor Liadova of Augustine's Station is a human that was taken over by one of the Jewels of Ymir.

It is safe to assume that, by the time of the events of the Augustine's Station campaign, he technically was not human at all anymore.

(Since the name of the xenos that possessed Liadova is unknown, he is referred to simply as Liadova throughout this article.)

History
The history of Liadova the human is currently not known.

By the time Inquisitor Rhyn and his Deathwatch Kill-Team infiltrated the Augustine's Station, Liadova had been in power for hundreds of years, and had even managed to enslave a few other key leaders with other Jewels, creating a relative peace between several xenos species normally unheard of throughout the rest of the galaxy.

The man
Liadova was obsessed with collecting xenos artifacts.

This obsession definitely started before he was taken over by a Jewel of Ymir, as it was one of the artifacts that Liadova discovered. Using this obsession as a cover, the "new" Liadova fervently hunted for more of the Jewels, and was believed to be attempting to restore his ancient people to power again in the galaxy.

However, his true intentions were never fully known.

Apparent death
Governor Liadova was eventually defeated and "killed" by Inquisitor Rhyn's Deathwatch Kill-Teams.

However, instead of attempting to destroy the Jewel, Inquisitor Rhyn kept it, and used it to overcome a new host in the hopes of interrogating the xenos that possessed the Jewel to find more information about the location of the other lost ones.

The xenohost
The new "xenohost" cooperated to some degree, although it remains unknown whether it was willingly or because of the Inquisitor's methods. Liadova revealed the energy signature of the ancient xenos ships so that the Inquisitor could find one and discover any information in their data banks on the possible locations of the Jewels.

By the end of the Space Hulk: Deathwatch campaign, Liadova escaped his imprisonment, activated the xenos vessel at the heart of the Space Hulk, and attempted to escape.

Disappearance
Inquisitor Rhyn's Deathwatch frustrated his plans again, destroying much of his ship and forcing him to flee aboard a smaller escape vessel. Iron Priest Jan Jansen then teleported aboard his craft and confronted Liadova, and after a short skirmish killed his new host body. What happened after that is unknown, including the current status of the Jewel that contained Liadova's essence.