This interdisciplinary, descriptive, library based research adopts Mark Elin’s theory of “Personality Disorder” to study William Dorrit’s character, whose title in the novel is the “Father of Marshalsea”. Elin’s theory of personality disorder is based upon the functions of “self-memory”, of which “Reality Testing” is an important one. Applying this theory, the research shows that in the first book of the novel, William Dorrit’s personality disorder vacillates between Narcissism and inferiority complex. In the second book, however, his personality disorder turns into “Posttraumatic Stress Disorder” which is caused by the overwhelming events of the past. Realitytesting, does not operate properly in William Dorrit’s mind. Consequently, he is not capable of making distinctions between memory and reality. The final outcome of this incapability is his complete mental breakdown. The other finding of this research is the existence of a structural symmetry between chapters nineteen of both books of the novel, in which the major themes are William Dorrit’s mental and psychological agitations.
