"Sybil" was the pseudonym of Shirley Ardell Mason, who was born January 25, 1923, in Dodge Center, Minnesota. Her parents were Walter Mason and Martha Alice Hageman Mason. According to the book Sybil, as a child Mason suffered from extreme abuse at the hands of her mother. Childhood friends commented in a recent documentary that Mason's home life and relationship with her mother seemed strange and unusual.
In the early 1950s, Mason moved to New York City to pursue graduate studies at Columbia University. Plagued by blackouts and breakdowns for many years, she began seeing a psychiatrist, Dr. Cornelia Wilbur, who eventually diagnosed Mason with Multiple Personality Disorder. Wilbur discovered 16 different personalities within Mason and believed they were a result of severe child abuse. During 11 years of therapy, Wilbur and Mason worked to integrate these personalities into one complete self, and afterwards Mason found she was content and well adjusted.