Mary Reynolds (1785–1854) was a 19th-century Pennsylvania woman considered the first, and perhaps most famous, American case of multiple personality disorder (now Dissociative Identity Disorder). Beginning in 1811, she experienced profound, alternating shifts between a melancholy, quiet personality and a lively, intelligent, but child-like one for 18 years. 

In my latest mystery/suspense tale, I permit my villain to possess this disorder. In that manner, she may sometimes sound like a woman and sometimes like a man.

Key aspects of Mary Reynolds’ case include:

• The Transformation: After waking from a long, deep sleep, Reynolds appeared to have lost all her memory, including how to speak, read, and write, yet she possessed no knowledge of her former life.
• Personality Shift: She switched between two distinct personalities (or “double consciousness”):
  • Personality 1: A reserved, somber, quiet spinster.
  • Personality 2: A cheerful,, curious, socially active, but naive, “child-like” person.
• Medical Documentation: Her case was documented by Dr. Samuel Latham Mitchell in 1816 and later analyzed by other experts, shaping early understanding of dissociative disorders.
• Context: While early accounts focused on her “fits” and loss of memory, later interpretations suggest her condition may have been a response to traumatic childhood events, including religious persecution.
• Significance: Her case was crucial in the history of psychology and psychiatry, as it provided a concrete, documented example of “dual personality” before the formalization of the term. 

Mary Reynolds’ case is often cited as a pivotal moment in understanding the development of the human mind and its capacity for fracturing under immense emotional or psychological stress. 

This transcript comes from Mary Reynolds: A Case of Double Consciousness by S. Weir Mitchell, M.D., Philadelphia, Wm. J. Doran, Printer, 1889. “Mary Reynolds was born in England in 1793, and, when four years old, with her father and mother and their family, they left their home in Birmingham to settle in Pennsylvania. Leaving in New York the remainder of the family, the father and son started out into the wilderness and chose a spot on the banks of Oil Creek in Venango County. The whole surrounding country was an unbroken forest. Twelve miles southward were the few inhabitants of Franklin, while six miles to the north lived Jonathan Titus, the proprietor of the land on which Titusville now stands. In this remote spot, William Reynolds and his young son built a log-cabin, in which the father left the lad while he returned to New York to bring the remainder of the family to their new home.

“For four months the boy remained alone in the cabin, rarely seeing the face of a white man, but being
frequently visited by Indians. In due time, the Reynolds family arrived, and with them the daughter Mary. Her childhood and youth appear to have been marked by no extraordinary incidents. She is said to have “possessed an excellent capacity, and to have enjoyed fair opportunities to acquire knowledge. Besides the domestic arts and social attainments, she had improved her mind by reading and conversation. Her memory was capacious and well stocked with ideas.” Though in no respect brilliant, she was thoughtful, and seems to have been endowed with an uncommonly good physical organization.
Her natural disposition tended to melancholy.

“Her spirits were low. She never gave herself to mirth, but was sedate and reserved ; she had no relish for company, but avoided it was very fond of reading what few books were to be had. She loved to retire to some secluded place where, free from interruption, she read and meditated upon her Bible, and
where she was apt to give herself up to prayer and devotional exercises.

“When about eighteen years of age she is said to have become subject to occasional attacks of “fits;” these were certainly hysterical, but of their precise characteristics no account is given. However, on a Sunday in the spring of 1811, she had an attack of unusual severity. It occurred while she was in a
secluded place reading and engaged in her devotions. Owing to her protracted absence, her friends became alarmed, and after a long search found her in a state of insensibility and in convulsions. The restoratives applied were not very successful. When she recovered consciousness (probably on this same
day) she was found to be both blind and deaf, and continued in this state for five or six weeks. “

From “Historical Conceptions of Dissociative and Psychotic Disorders” Wiley Online Library: “The most influential early case of dual personality or multiple personality disorder (MPD) was that of Mary Reynolds, first published by Samuel Latham Mitchell in 1816. The growth of interest in hypnosis, which eventually followed Mesmer’s animal magnetism, marked a systematic secularization of interest in phenomena previously ascribed to the Devil and his minions. The first use of the term ‘dissociation’ in the medical literature was by Benjamin Rush (1818), who used the term to capture the alterations in mood states and their seemingly disconnected appearance in what is now called bipolar disorder.”