"Emissary of the Gods"
"It is my duty to record this momentous occasion. Our prayers have been answered – we have been blessed, to an emissary of the gods in our humble observatory. He is known as Gusion.
His appearance is startling, but we are but mere mortals, it is understandable that we would have such a reaction. Three heads are beyond human. To describe them in more detail would be insulting to him, if not blasphemous.
Already, we have felt Their guiding hand, helping us discover the mysteries of the cosmos, the secrets within the stars. Saqqara is truly blessed by their teachings."
~ Saqqaran tablet, recovered in The Scale of the Problem
Gusion, a Goetia Demon, servant of the Teacher of Teachers, was sent as an Emissary of the Ancient Entities to the Saqqaran people. It seems the ancient people held him in high reverence. His appearance resembles a baboon except he has three faces: one where you'd expect a face to be and two protruding from each side.
Presently, he haunts the halls of the Saqqaran Observatory, where he uses visions and telepathy to communicate with any visitors.
A giant gate bears his likeness with three alcoves intended for offerings. Perhaps, this is where Gusion himself is sealed.
First encountered during Operation Desert Lotus, Gusion interrupted Thanja's seance by appearing in her mindscape and breaking her index finger. Even suppressed he is dangerous.
It is possible he is the one subjecting the Kobolds stuck at the Observatory to various visions and the one who offered the party in The Scale of the Problem temporary knowledge of the Saqqaran language after performing a flame ritual.