I can provide general information about DID and how the first alter or part is typically formed. Dissociative Identity Disorder (formerly known as Multiple Personality Disorder) is a complex and rare dissociative disorder in which an individual's identity becomes fragmented into two or more distinct personality states, commonly referred to as alters or parts. These alters can have their own unique characteristics, memories, emotions, and behaviors.
The development of different alters in individuals with DID often begins in response to severe and ongoing trauma during childhood, especially when the trauma occurs before the age of six. The dissociation is considered a coping mechanism that allows the person to compartmentalize the traumatic experiences, preventing overwhelming emotions from flooding their consciousness all at once.
The first alter that emerges is usually referred to as the "host." The host is the identity that is most often present in everyday life and is typically unaware of the other alters initially. As the trauma continues or recurs, other alters may begin to form as a way of managing the traumatic experiences.
It's important to note that the experience of DID can vary significantly from person to person, and the specific details of how and when different alters emerge can be unique to each individual's history and circumstances. Therapy, particularly specialized approaches such as Trauma-focused therapy and Dialectical Behavior Therapy (DBT), can be beneficial in helping individuals with DID explore and integrate their various identities to achieve a more cohesive sense of self.