The NPC is an archmage called Radoc who hails from New Empyrea on Oerth! That's the Aquaria subsetting!
Here is what Forgotten Realms Wiki has on Radoc:
What did Radoc get up to in the Aquaria adventures?Forgotten Realms Wiki wrote:Radoc, also known as "The One" and Doc, was a powerful archmage dwelling in the Star Mounts in the High Forest around 1358 DR.
The mysterious charismatic figure known as Radoc gave the appearance of a peaceful yet powerful healer, seldom seen traveling yet known to give aid to those in need, such as to the folk of Loudwater. What wasn't known was that Radoc was had been exiled from another Prime Material Plane.
He had been marked with a glowing sigil by the titan Sylla.
His goal was to return to his home, New Empyrea, as its master. He slowly built a power base in the Star Mounts, using tribes of mongrelmen for muscle while purchasing all of the mithril that the orcs of the Spine of the World could mine.
His faith was that of Tangg, an other-planar power.
Radoc was a character in the Egg of the Phoenix modules for the New Empyrea setting.
What sort of trouble could he cause back on Aquaria with a bunch of mongrelmen and a ton of mithril?
What was Jennell Jaquays mechanism for moving Radoc from New Empyrea over to Faerun? Was that a one of event or could other Aquarian NPCs arrive in the Star Mounts?
What sort of mechanism was Radoc hoping to use to return to Oerth? Does he actually have a plan formulated in FR5?
Do you think he would fall in with PCs that knew about spelljamming or planewalking? Or do you think he would work agaisnt them and try to steal their secrets?
Is Radoc a good way to move Forgotten Realms PCs over to New Empyrea?