Boreas was presumably first inhabited by the Judgers. For an unkown reason they left Boreas but left an artifact behind. It is possible that the Judgers never inhabited Boreas in the first place, but hid the artifact there to prevent others from taking it.
Many years later Boreas was discovered by the Dominion. They used it as a prison planet for human prisoners. The prisoners were able to escape and take control over most of the planet. Later on the Dominion discovered the presence of a Judger artifact on Boreas. Kal was also tasked with finding this artifact but was too late as the Dominion captured it and took it to Volteron.
The fate of this planet is unkown.