Adeptus Custodes - The Shadowkeepers - Wardens of the Dark Cells: There are terrible things locked away beneath the Emperor's palace, eldritch terrors from the depths of Old Night that could annihilate the Imperium. To the Shadowkeepers falls the duty of standing guard over them unto the end of time. The Shadowkeepers hold the keys to the rune-locked portals hidden deep beneath the Imperial Palace. They alone know the ways by which the runic locks may be disengaged, the wards unbound and the sanctic circles breached. They alone know that these things must never happen, for the Dark Cells hold such horrors at bay that Mankind's sanity would not survive their release.A full Shield Host is devoted to this grim responsibility, over a hundred Custodians patrolling the dark and silent corridors, vigilantly watching over the last terrors of Old Night. It is a task that would soon drive most men mad, for though neither sight nor sound can escape the forbidden cells, the air of those corridors is charged with dread.A perpetual menace thickens the shadows and makes them crawl. Even the superhumans of the Adeptus Custodes are forever on edge in those dark oubliettes, for the sense of unspeakable threat never wanes. It is a testament to the discipline and spiritual fortitude of the Shadowkeepers that they stand their guard unflinching, sometimes for solar decades at a time.The ranks of this shield host include many Custodian Wardens, whose oaths of protection help them to focus upon the task at hand to the exclusion of all else. The leaders of these forbidding sentries carry ancient weapons of mysterious provenance, their use intended as a last resort should anything ever break free from the Dark Cells.For ten thousand Terran years the Shadowkeepers have performed their duty, yet the coming of the Great Rift changed everything. With the power of Chaos spilling raw and seething into the spaces between the stars, new abominations have come to light. Worse still are the cells that stand suddenly empty, the entities and artefacts once contained within spirited away by some unholy force to curse the galaxy once more. Fearing the consequences of such dread remnants of the Age of Strife falling into the wrong hands, the Shadowkeepers at last sent warriors out into the galaxy. These jailers must trammel that which should not be, slaughtering all who seek to impede them, before returning their foul prizes to the cells where they belong.There have been many Shield-Captains charged with mastery of the Shadowkeepers. This appointment confers the title of Lockwarden, a name that is borne in perpetuity and garners solemn respect from every other member of the Ten Thousand. The Lockwarden must be the sternest of all guardians, the most unrelenting and alert gaoler on the face of Terra. Moreover, should any creature or relic escape the Dark Cells, or newly emerged threat need to be imprisoned therein, it is the duty of the Lockwarden to personally oversee the operation.The current incumbent of this position is Shield-Captain Borsa Thursk, who has been Lockwarden for a standard century and a half. He is a grim and frighteningly intense warrior whose utter fearlessness and steely vigilance make him ideal for his role. It speaks volumes about the dire condition of the galaxy that Thursk left Terra but twice before the breaking of the storm, yet he has barely set foot there since the Great Rift yawned wide.