Human (Earth)

First appearance: 

The Forgotten Age I: Soulfire

As far as can be deducted from Z's first Journal, he is living in a time period that is either present or in the near past. The name of the hospital that Z is writing in is the Mark Twain Memorial hospital, which could be a clue as to when these journals were written.

More information becomes revealed in Resolution, where the patient learns the truth about his origins, and uncovers the mystery of what is really going on...