The Cornerstone of the Galaxy, also called The Cornerstone, was a powerful artifact located in a hidden Jedi temple. Jedi Master Bobarian Afol studied it on Aliston Nor. He eventually came to remove the Cornerstone from the temple, resulting in his galaxy to change drastically. In this new galaxy the Cornerstone temple reappeared on Fennesa, where Afol reinserted the Cornerstone. Some time later, the nerf herder Sig Greebling unearthed the artifact, and the galaxy became mixed up.[1] Greebling and Afol then went on a quest to lock the Cornerstone into it's place in the new galaxy.
Appearances
LEGO Star Wars: Rebuild the Galaxy — "Part One" (First appearance)
LEGO Star Wars: Rebuild the Galaxy — "Part Two"
LEGO Star Wars: Rebuild the Galaxy — "Part Three"
LEGO Star Wars: Rebuild the Galaxy — "Part Four"
LEGO Star Wars: Rebuild the Galaxy - Pieces of the Past — "Part One" (Mentioned only)
Sources
Get Ready for Darth Jar Jar, TIE-Wings, and More in LEGO Star Wars: Rebuild the Galaxy on StarWars.com (backup link)LEGO Star Wars: Rebuild the Galaxy | Teaser Trailer | Disney+ on the official Star Wars YouTube channel (backup link) (First mentioned) (First identified as Cornerstone)
"Launchpad" — Star Wars Insider 226