As a child your parents told stories of Rovagug and his world destroying minions. It kept you eating your vegetables and brushing your teeth before bed.
Over the years you grew, matured, studied. And then, you realized that you no longer feared such creatures from your childhood nightmares. Now you feared for what they could do for the people. Your family, your village, your kingdom, the world. And you could do something about it.
Sometime ago (at least a decade) you were approached by a being that offered you membership in a inter-planar group of protectors, known as the Custodians of the Membrane. Yes, it's a cheesy name, but it was there before your ancestors learned to use a wheel.
An elite force of powerful entities from the various planes who have dedicated themselves to ensuring the planes of the world remain in a state of dynamic equilibrium. Without their careful maintenance the Planes and their inhabitants would be overwhelmed and unbalance each other, merging and falling back into the chaotic nothingness from whence all of Creation sprang.
The Custodians cite their origins as shortly after the Great Beyond arose, when the (then) young gods of the cosmos discovered that there were Beings in the spaces between the planes, powerful and incomprehensible enough to drive even them mad and destroy them. In fear the gods agreed to work together, to create a singular membrane that would keep the Maelstrom at bay. At first, there was no need for custodians, but neglect and inattention took their toll, as the gods turned their minds to conflicts over what the interior of the single realm they had protected should be like. Eventually a breach occurred, and a god traveled outside it. What he encountered there would shake his very nature.
When he returned, he fashioned the Worldweavers of the titans to keep the horrors he had experienced at bay. It was they who died in droves seeking to recover the portions of the realm that had been lost, and discovering that to be futile, it was they who conceived a bold and audacious plan by which the rest of the realm might be saved.
And so the three eldest of them, the last to survive walking into the Maelstrom and whatever they encountered there, journeyed to the Membrane the gods had made, where it still remained, and pulled it inwards, twisting and pinching it until they had formed an arrangement where the incursion was contained. It was a change too drastic for the gods to ignore, as new boundaries sprung up, and powers were constricted. When at last the gods came upon the Worldweavers, they were told that if the changes were undone, so they and all they valued would also be. "Look upon the cocoon we weave." said the eldest of the Worldweavers "And know it for what it is... our tomb, woven of our own flesh and souls, to keep you safe. For it, we extract a price... that your realms will be divided, your powers forever more constrained and your influences limited. This is how it must be, if it is to be."
The gods, it is said, did not see the wisdom of this, but did see that the changes were beyond them to undo less they worked as a whole again... and each of them had made enemies they would not trust enough to work with again. The Worldweavers went into their tomb, set at the center of the newly arranged planes, and were forgotten to time with their passing. The gods decided to set up a watch upon the membranes of the planes, so that each might know of any other's attempt to unbalance and pierce them. And so the Custodians were created.
Astrarium, the city of the Custodians, carved into the dead husks of the Worldweavers that surrounds Groteus and keeps the entity therein at bay, for Groteus is said to be what was created when the Maelstrom's intrusion was cut off and isolated. This was to be your home as a Custodian. Unfortunately, Astrarium was cutoff from all. It has been several years since you have had any contact with a Custodian other than a few scattered about Golarin.
