From what the Council's been able to discover from the book of Tarnis and, and, and other sources, Glory and two of her fellow hellgods ruled over... one of the more seriously unpleasant demon dimensions.
Rupert Giles[src]

The Book of Tarnis was an ancient book that held information on Glorificus and The Key. It was written by Tarnis himself.

By the year 2000 and 2001, the Book of Tarnis was under the possession of the Watchers Council.