Board Thread:Theories and Speculation/@comment-26127155-20150608044937/@comment-25319479-20150609091745

My theory is that Shin was a human experiment that Orochimaru created when he was part of the Akatsuki, and after his departure, Obito took him in and gave him access to his sharingan collection. With the knowledge of how Orochimaru created him, Shin used it to create replica's of himself to further aid his cause.