Crucible, known as Crucible Prime during the days of the Sith Empire, was a planet in the Cruciatus system of the Sith Worlds in the Outer Rim Territories. Thousands of years before the Battle of Endor, it was ruled by a Sith Lord named Darth Drear who built his temple in the Barrens.
After the collapse of the Sith Empire, Crucible was left to its own devices until the rise of the Galactic Empire. It was then recaptured by the Sith as part of the Empire's efforts to subjugate the Outer Rim. During which time, the planet was used as a location for developing the secret Project Blackwing.
Later, the Empire too would fall, and the First Order would rise out of its ashes to keep the peace on Crucible.
- Star Wars: Legacy of Evil (First appearance)