Catacombs of Wrath - Rise of the Runelords

From Page 24 of the Rise of the Runelords Volume 1: Burnt Offerings. This site was originally a laboratory and prison run by a cruel
man named Xaliasa, a man who had given his soul to the demon Lamashtu in return for eldritch and dark powers. He was a thaumaturge in the service of Runelord Alaznist, but unknown to her, Xaliasa was also a secret assassin pledged to Karzoug. Working as a double agent eventually drove Xaliasa mad, and he came to be known to his minions as the Scribbler. He perished in the now inaccessable lower levels of the Catacombs when Thassilon fell and Alaznist’s empire sank under the sea. Yet not all of his minions perished—his quasit familiar Erylium survived.