(Name translates directly from ancient Egyptian as: Strong Protector, the Hidden One.) A mysterious shaman appearing without regard to wheres and whens, upon the divine bidding of other Realms. An entity of legend, belonging to a legendary and ancient sect.
(Apologies to GRRM and HBO)
A group of northerners want to bring the Old Gods back to the south. They grow cuttings from the white trees seeking the blessings of the Old Gods on the project, and when the saplings are big enough, they carve faces in them and secretly plant them in forests all over the south, to extend the 'reach' of the Old Gods.
The plan works of course, but the trees are *baby gods*, and behave as such when invoked.