Who is Mr. Shaitana from Cards on the Table and what is their importance?

Mr. Shaitana is a wicked man who purposefully adopts external characteristics of Mephistopheles, the devil. Shaitana has no compunction about delving into the past lives of people and discovering anything that he can about them that would be an embarrassment in their future. His greatest skill is inviting the confidences of women, coaxing them to share their greatest secrets with him.