HeadMate
An alternate personality or identity living in your head. Similar to a roommate or a house mate, but inside your skull. A person who describes themselves as having headmates is saying that they have people living in their heads who they have conversations with.

Some people can claim different ethnicities or sexualities, thus allowing them to join an autonomous caucus (for instance queer or women’s) that they were not otherwise entitled to join.

When they are acting as the personality of one of their headmates, they call this "fronting"

Related to Otherkin, Multiple Systems, and Tumblr social justice activist
I was so out of it I blacked out and one of my headmates took over and drove the car home.