Voran

From Syra D&D Wiki

Voran was a powerful Estorian wizard who, following the Illithid War, settled with some of his people across the sea in the Dawning Woods, where he built a number of sanctuaries for himself and his research by magically carving them out of the earth itself. It is unknown what became of him, but his ghost was recently seen in the ruins of Estorium, having been driven mad.

At some point, he wrote a book detailing what he had learned about the illithids.