Seraphim of the Abyss

The Gryphon Knights are a mysterious and ancient Dark Angels Successor Chapter from the 2nd Founding, and thus members of the Unforgiven, Scions of the Lion that hunt the Fallen Angels. However, unlike many of their brother Chapters, the Gryphon Knights have an established Homeworld in the form of a Feudal World named Boletaria, yet still actively engage in the Hunt for the Fallen. They also have developed their own distinct cultures and beliefs over the millennia inhabiting the planet that was once heralded as a "New Caliban."

History
During twilight years of the Great Crusade, a small contingent of the Dark Angels Legion, more specifically, the Gryphon Knights Chapter, under the command of Master Lordin Tolken, discovered a world previously overlooked by the Imperium. This planet, Boletaria, as it would become known, had a history akin to that of the Dark Angels' home of Caliban.

Boletaria’s human population had, after millennia of degradation in the Old Night, had their technology reduced. They were also plagued by another misfortune- beasts afflicted by the Warp. During a particularly horrid Warp Storm near the planet, the wildlife of Boletaria was affected by the chaotic taint of the Immaterium whilst the now Feudal humans had established cities in the shadow of great mountains, hidden from the Warp Storm’s effects until it passed.

However, these Beasts would develop a maddened hunger for human flesh and assaulted the many mountain-fortresses of humanity across Boletaria. Thusly, orders of noble warrior hunters were formed after years of sustaining siege by savage monsters to slay the Beasts before they could threaten their respective homelands. And so, greatly intrigued by the coincidence of stumbling across another world like their own, the Chapter of the First Legion brought low the Beasts of Boletaria and began the process of bringing the planet into compliance, before the Great Heresy had begun, and the galaxy was split by the Ruinous Powers.

During the events of the Horus Heresy, the Gryphon Knights were stranded upon Boletaria and while most were uneasy about the state of the Warp, some found the familiarity of Boletaria to grow on them. And many years later, when reunited with the rest of their Legion, and told of both the Emperor's fate, and that of Caliban and the Lion, the Gryphon Knights all took vows of shame that they were unable to lend their blades against the treachery of the former Warmaster or Luther's conspirators.

When it came time to break up the Legions, the Gryphon Knights parted from the Dark Angels and claimed Boletaria as their Chapter Homeworld. They had recruited a fair number of recruits from the planet already, and the Knights were determined to not lose another home again. And to further keep the legacy of dead Caliban alive, the new Chapter maintained the patterns of Power Armor worn by the Legion during the Crusade, proudly keeping the traditions of the First alive in their own manner.

But thoughts of preservation would turn to vengeance as the knowledge of the surviving Fallen Angels reached the Sons of the Lion and the Unforgiven was formed, the Gryphon Knights merrily joined the Hunt to persecute and take vengeance for their first home lost, and their gene-sire's disappearance.