The Celestial Worthy of Heaven and Earth

"King of Space-Time;
Beacon of Destiny;
Embodiment of Sefirah Castle;
Dominator of the Spirit World;
Lord of Mysteries."

The Celestial Worthy of Heaven and Earth refers to the former Great Old One, Lord of Mysteries, who was the most active on Earth from the Pre-Epoch to the middle of the First Epoch, and the former owner of the Sefirah Castle. "He" is also referred to as "The great ruler of the spirit world" by the Seven Lights.

The Transmigrators were a part of the Celestial Worthy's resurrection plan.
(Source: Lord of Mysteries | Circle of Inevitability Wiki)