"Alter egos" and "dissociative identities" are related terms, but they refer to different concepts.
Dissociative Identities (DID): Dissociative Identity Disorder (DID), formerly known as Multiple Personality Disorder, is a complex and rare psychological condition characterized by the presence of two or more distinct identities or personality states within an individual. These distinct identities are referred to as "alters." Each alter has its own unique set of behaviors, thoughts, memories, and experiences. These identities can have varying ages, genders, and even physical characteristics. The switches between different alters can be involuntary and may be triggered by stress or trauma. Individuals with DID often experience memory gaps or amnesia for periods when a different alter is in control.
Alter Egos: The term "alter ego" is often used in a colloquial sense to describe a different aspect or persona of a person, especially in popular culture. It refers to a secondary self, a distinct identity, or a hidden side of an individual that may be quite different from their usual personality or behavior. In this context, it doesn't necessarily imply a dissociative disorder. People may adopt alter egos for various reasons, such as in performance arts, creative expression, or online personas. It is a concept that is not exclusive to dissociative disorders and can be seen in many forms of self-expression and identity exploration.
In summary, "alter egos" are personas or aspects of a person that may be adopted voluntarily or for specific purposes, whereas "dissociative identities" are distinct personalities that emerge as part of Dissociative Identity Disorder, a dissociative disorder with involuntary switches between identities, often resulting from traumatic experiences in the person's life.