They were not created. They condensed. Wherever two states of existence press against each other, the boundary develops a logic of its own. That logic, given enough time and pressure, becomes aware. Awareness at a boundary becomes a presence. And a presence with sufficient weight and purpose becomes a Gate Keeper.
The Gate Keepers are ancient beyond any mortal reckoning. They existed before most of the realms they guard borders between. They are not divine, though gods treat them with caution. They are not creatures in the way a wolf or a demon is a creature. They are the Multirealms' own mechanism for ensuring that the gradient doesn't tear itself apart.
Every spell that crosses planes, every soul that departs a body, every prayer that reaches a god - all of them have passed, unseen and unaware, through a Gate Keeper's consideration.
What They Embody
Each Gate Keeper is a threshold - a metaphysical junction between states of being. Life and Death. Sleep and Wakefulness. Form and Spirit. Time and Eternity. Ignorance and Revelation. Dream and Waking. Truth and Illusion. There are dozens of these junctions, perhaps hundreds. Most mortals pass through several without awareness.
What They Are Not
They are not judges in the moral sense. They test readiness, resonance, and capacity - not goodness. A deeply good person might be turned back from a divine realm not because they are unworthy but because they are not prepared for the resonance shift. The Gate Keeper turns them back for the same reason a doctor sends a patient home - not as punishment, but because arriving where they intended would destroy them.
Encountering a Gate Keeper
Most planar crossings carry their own resonance as a key. Teleportation spells encode a destination and a purpose. Divine spells carry the authority of the deity who granted them. The Gate Keeper reads this resonance and, satisfied, allows passage without manifesting at all.
A Gate Keeper manifests when the key is insufficient or absent. The manifestation varies - some appear as figures of geometric perfection, others as monstrous reflections of the traveler's own fears. Some manifest as pressure only - the sense of something vast considering whether to allow you to continue.
The encounter is always a test, never a battle. The answer does not have to be impressive. It has to be true.
Use Gate Keepers sparingly. Their power as a storytelling tool comes from their rarity. Not every teleport. The moment a character returns from death and the Gate Keeper has something to say about it. The moment a party crosses into a divine realm and the Keeper makes clear, without hostility, that entering changes them.