Dantalion is a demon described in the grimoire The Lesser Key of Solomon:

"The Seventy-first Spirit is Dantalion. He is a Duke Great and Mighty, appearing in the Form of a Man with many Countenances, all Men's and Women's Faces; and he hath a Book in his right hand. His Office is to teach all Arts and Sciences unto any; and to declare the Secret Counsel of any one; for he knoweth the Thoughts of all Men and Women, and can change them at his Will. He can cause Love, and show the Similitude of any person, and show the same by a Vision, let them be in what part of the World they Will."

(Source: http://www.sacred-texts.com/grim/lks/lks05.htm#page_45)