Each alter is unique with it's own way of being. Particular items such as age and gender, as well as behavior are indicative of what the person needs to integrate.  When talking about structural dissociation we refer to alters as either apparently normal parts (ANP), emotional parts (EP), and the observing emotional part (OEP). The ANP is often in the role of host, while the EP is the part that holds trauma memory. The observing EP is the part often though of as the ISH.
Types of Alters
The three types of protector alters
• Fight alters respond to both internal and external perceived threats. They are defensive and avoid attachment, dependence and emotional needs.  They will often inflict injury upon themselves and others in the system, including the host and they usually have an unrealistic view of their power to protect. 
• Persecutory alters often cannot tell an inner threat from an external one and can believe themselves to be the original abuser, acting out the drama by abusing others inside as they perceive their original abuser would have done. 
Both of these types of protectors are responsible for what is commonly seen as eating disorders, substance abuse, self harm and other destructive behaviors. In adulthood, the protectors perspective changes and they see the various states that act as host to be the threat, instead of the original abuser who is probably out of their life at this point. Their primary function is still to protect the system, but now they protect against the host. They have the ability to use many methods to stop anything they perceive as a threat to the system. 
• All other protectors tend to be caretakers, who for the most part, focus on the care of others, both inside and out and they tend to neglected their own needs. Caretakers are introjects, real or fictional, of who the child perceived as caring. These parts are usually named after who or what they represent. 
Alters in the role of an introject
An introject is a construct formed outside of consciousness, created some time ago, which consists of two parts: a child part and the "mask" of the introjected part. We can safely assume this nature for hostile introjects. Hostility is always an acquired trait. More than that, it always has an altruistic goal: system protection. 
Other typical alters
The identity of each part created in childhood was influenced by the relationship with the original abusers, yet the types of alters seen in people with dissociative identity disorder fit into certain descriptions such as: twin parts, who might be seen as good and evil, and those with deformities and handicaps, where the handicap. The handicap might represent a forbidden act such a listening, talking or seeing.  Also common are animal and inanimate objects as alters. 
Many alters are "stuck in trauma time.  Due to this they are exiled" by others in the system; others that do not want to hear or know of the trauma.  Some alters can be pushed so far from consciousness, that other alters think they are dead. Alters cannot be killed however, so these parts can be brought out to be worked with at a later date. 
Inner-self helpers (ISH) - Observing EP
These parts might just be the most interesting of all. They might appear savant like, but keep in mind that they can only answer the best they can. Consider a confident child who will correct others when they feel they are right, but this confidence does not make their answer any more correct. Some ISH's appear robot-like, while others are angel-like and so on, but however they present, they usually know they are the ISH, and that their job is to observe the inner world. They do not normally come out until they are directly coerced to do so.