Not much is known about the Gatekeeper, only that she predates the creation of the first universe. She possibly became a permanent resident of the Graveyard after her birth, which she either guards or oversees. As the universes died and their remnants became part of the Graveyard, she became an inhabitant of a region in the Graveyard known as Beyond Shades. There, she lived on a Victorian styled house which was placed on the edge of a cliff, overlooking a small beach and the apparently endless ocean.
She was one of the Perennials which were neutral during the initial phases of the Protomachy, and she believed herself to be above such conflicts. However, contrary to her beliefs, the Gatekeeper joined the war against Ayavan, but only for a short time. She remained the rest of the war in near-total neutrality, and was one of those who did not interfere with Emperor Hadrian's restoration of the Tower of Dawn, as he was on the opposing side. She ultimately considered the restoration and second activation of the Tower of Dawn to be a better outcome than any other possible ones.
Shortly after the end of the Protomachy and during the Hollow Tomb Crisis, she met Harry when he appeared on Beyond Shades after the young wizard unknowingly destroyed one of the levels of the Graveyard. She explained to him what exactly was happening and a few details regarding the Twelfth One, leading to her commanding Harry to recover the pieces of the Achronal Key, so that they could unlock the Hollow Tomb and discover what exactly was happening with the Twelfth One.
- The writer of the story has affirmed that the Gatekeeper was based on Missy, a character from the British TV series Doctor Who.
King of Kings, Ruling Over Rulers (mentioned only)