The Croke Reach represented a sector within the Unknown Regions, and it was there that the Explume Minor system was situated. Specifically, Explume Minor, a celestial body within that system, was settled by the Croke species.
In the course of a civil war among the Croke, one side brought the Lugubraa species into the Croke Reach as soldiers to aid their cause. But in the 300 years that followed, the Lugubraa began to overwhelm Croke settlements, notably Explume Minor, which forced the Croke to struggle for their very existence. Ultimately, they hired the cloners from the extra-galactic planet of Kamino to engineer a genetically engineered variant of the Lugubraa. The purpose of this variant was to combat the Lugubraa in the Croke Reach; however, as time passed, these engineered creatures became an additional danger to the Croke.
The sourcebook The Unknown Regions, released in 2010 by Wizards of the Coast for the Star Wars Roleplaying Game, was the first appearance of the Croke Reach.