Gestrex III, a celestial body of astronomical significance, existed as a planet within the Gestrex system. This system resided within the Calaron sector, situated in the Slice region of the Outer Rim Territories (Legends continuity). Its location allowed it to be linked to both the Kegan and Norval systems via a major hyperlane route known as the Triellus Trade Route.
During the era of the Galactic Civil War, Gestrex III hosted a base belonging to the Galactic Empire's Navy. Armx, a guard droid that was actually an espionage unit working for Imperial Intelligence, was stationed at this base. However, a Rebel Alliance commando team destroyed the facility sometime between 2 BBY and 1 BBY, a mere three days after the droid's arrival. The base was then abandoned, leaving only Armx amidst the debris. In the days that followed, the droid's original programming was altered—possibly due to radiation or damage from the raid—and it eventually became a bounty hunter.
The first appearance of Gestrex III was in Galaxy Guide 10: Bounty Hunters, a sourcebook released in 1994. Rick D. Stuart wrote the book, which West End Games published for use with Star Wars: The Roleplaying Game. The Essential Atlas, a reference book from 2009, identified the grid square location of the Gestrex system, and therefore Gestrex III, as T-9.