what is the core is one of those questions/answers that have many meanings because there are many different beliefs/cultures/locations and ways treatment providers approach the issue...

here where I live and work, NY USA, the mental health community believes the core is the person that was born to the body, the one from which the first alter was created from. here it is also believed the core and host is the same thing.

example I was the one born to this body, my alters were created / came into being because I could not handle being abused in such horrendous ways in which I was. therefore I am the core /the host in which all the alters resided.

other locations cultures treatment providers may believe differently.