During the initial stages of the Galactic War, Darth Thanaton issued a challenge to Lord Kallig, the former apprentice of the supposedly corrupt Darth Zash, to a Kaggath. Driven by his dread of Kallig's burgeoning strength, coupled with his disdain for anything related to Darth Zash, Thanaton instigated a competition between the two Sith, one that would pit their disparate power structures against each other. Neither party could withdraw, nor could they surrender; victory meant enduring glory, while defeat meant shame and a likely demise.
Despite the fact that Darth Thanaton possessed an unjust advantage, owing to his position as a Dark Council member and his significantly larger power base compared to Kallig, the ascending Sith Inquisitor promptly sought out new allegiances and strategic positions. Initially, the two Sith Lords avoided direct confrontation, opting instead to deploy their respective allies against one another. For Kallig, this entailed efforts to reconstruct the Silencer project, thereby securing the alliance of Moff Valion Pyron. With the Moff's backing, they successfully garnered additional military allies, whereas Thanaton concentrated on the allies he maintained within the Sphere of Ancient Knowledge. Eventually, as their clashes intensified, Thanaton's power base was systematically eroded by Kallig, with his allies either perishing or switching allegiance to Kallig's side, his strongholds demolished, and his schemes thwarted by the resolute Sith.
As the Kaggath neared its conclusion, Thanaton arranged a meeting with Kallig on Corellia, directly challenging them in the presence of other Sith and Imperials. Rather than confront a revitalized and fully prepared Kallig, Thanaton initially deployed Darth Kallous, followed by two armored guards, in attempts to assassinate Kallig, all of which were unsuccessful. Only after these failures did he personally intervene, only to be brought near to death by Kallig's lightsaber. Violating the established rules of the Kaggath, Thanaton retreated to Korriban and sought assistance from the Dark Council.
The Kaggath reached its dramatic climax when Lord Kallig defeated Darth Thanaton before the Dark Council on Korriban. Darth Mortis executed Thanaton as he desperately crawled towards his fellow Councilors, unable to help. Kallig was then bestowed with Thanaton's seat on the Dark Council and was personally granted the title of Darth Nox by Darth Marr.