Xanathar was originally a follower of Xantriph of Zhentil Keep. He was sent by the Zhentarim to Waterdeep to destroy the Lords of Waterdeep and establish a ruler allied to the Zhents. However, he soon started to act independently, establishing a new thieves' guild and disappearing. He later led a great thieves' guild and only his four lieutenants—Slan Thurbel, Slink Monteskor, Ott Steeltoes, and Shindia Darkeyes—knew his true nature and aspirations.
Xanathar greatly enjoyed been a crime lord just under the nose of the Waterdeep's Lords. Xanathar very liked finely prepared foods, scented oils, and spiced southern tobaccos and herbs.