Nematov is or was a great Stone Dragon who lived far below the surface of Mount Pillar in the Shadowfel, nearly at the point that the deepest vein of rock from the mountain had tapered away. She appears to have the ability to glide through stone as Balvan and Zora do, presumably due to her otherwise unseen Draconic subtype.
Balvan first encountered Nematov while exploring the depths beneath the mountain that is him in the aftermath of his battle with the great Gold Dragon Zoloto. In his state of fatigue and despair, he unburdened to her his sorrow over the loss of both his friend and the Fadelands portion of his home and asked for her advice. She told him to find something that makes him happy, revelaing that she spends her time creating intricate geometric sculptures from the patterns of density in the rock of the Underdark. This inspired him to create his breastplate.
Balvan returned to where he had met her when he sought advice on saving Alice, but the Dragon was not present, having presumably moved on.