Which times, was the origin of the reported case of a dissociative disorder and the dissociative identity disorder ?

I have a experience, that I read the case of "Billy Milligan" in a book, at the age of my childhood. About the later "coffin", I did not read. And, I have not experience, watch any videos ( on TV or the media) of the real patient.

However, I had some friends in personal reality, who having symptoms of DD ( I guess, they are not DID ).

Please, introduce to me, if there are a web page and a document serving as a reference.

Please put a URL link. It is OK, with just.

Thank you.