The Stewards of the Sanctum are a Dark Angels Successor Chapter.
They are very few in number and specifically hunt Necrons, as the Chapter seeks out any treasures that may be hidden on Tomb Worlds.
The following information is not to be regarded as officially sanctioned and/ or is not written from an in-universe point of view. A detailed explanation of the term "Trivia" as used in the Lexicanum can be found here.
The Stewards of the Sanctum were created by Steve Copp and they were featured in White Dwarf 489.