Ostor was a planet located at the fringe of the Outer Rim. It was a barren planet composed of red soil, deep canyons, and various wind-sculpted rock formations. In the aftermath of the Clone Wars, a Separatist holdout moved in to the planet, hoping to avoid the newly-formed Galactic Empire. By 17 BBY, however, the Galactic Empire had discovered their presence, and sent several of their forces in a military operation called the Shrouded Offensive to both wipe out the Separatist holdouts and conquer the planet into the Empire. However, due to at least three mistakes made by Darth Vader, the operation proved to be one of the most disastrous for the Empire.