A celestial body within the Core Worlds, Thomork housed an Imperial Military ship-building complex. In the time leading up to the Battle of Endor, this facility was responsible for the production of Imperial-class Star Destroyers. Sometime prior to the year 10 ABY, the Empire propagated a false story indicating that the Thomork shipyard had been shut down due to a viral epidemic. To give weight to this fabrication, they murdered in excess of 450 individuals at the site. Subsequently, the shipyard was secretly reactivated and utilized for clandestine Imperial manufacturing efforts, including the original World Devastator superweapon.
Thomork existed as a celestial object situated within the Thomork system, which itself was located in the Southern Core region of the Core Worlds.
In the period just before the Battle of Endor in 4 ABY, Thomork was the location of an orbital shipyard that exclusively produced Imperial-class Star Destroyers for the Galactic Empire. A settlement was also present there.
Years before 10 ABY, the Empire disseminated a rumor claiming that the Thomork shipyard had ceased operations because of a highly infectious new type of hive virus. To support this claim, Imperial operatives also killed over 450 residents of Thomork.
The settlement was deserted, and the system of Thomork gained a reputation as a location of mass killing, eventually becoming as notorious as the Dagobah system in the Outer Rim Territories. The Thomork facility remained structurally sound, and the Empire secretly re-opened the shipyard, repurposing it for highly classified construction projects, including the Silencer-1, the first World Devastator superweapon of the Empire.
The Dark Empire Sourcebook from 1993, written by Michael Allen Horne and released by West End Games for their Star Wars: The Roleplaying Game, was the first to mention Thomork. The Essential Atlas, a reference book from 2009, placed the Thomork system, and therefore the celestial body of Thomork, in grid square L-12.
A map included in the 2012 book The Essential Guide to Warfare mistakenly identified Thomork as "Tomark." The Essential Atlas had previously introduced that proper noun as the name of a star system within the Mid Rim, based on the name of the planet Tomark II, which was introduced in "The Ando Project," an RPG adventure published in November 1996 in the eleventh issue of the Star Wars Adventure Journal.