OH MAN I am canonblind but fascinated and delighted. John is weirdly well-suited to, uh, this extremely specific form of identity horror! He's a fragment of an eldritch entity/malevolent god/Cthulhu-tier Great Old One who lost his memories and got shoved into the body of a mundane middle-aged detective. He spent a month helplessly, voicelessly bound to a hospital bed, where the kind nurses called him John Doe. He took that as his name, became buddies with the man he was possessing, and has been struggling between the identities of "John Doe, really into art and poetry, willful amnesiac" and "KING IN YELLOW, FEASTER FROM AFAR, DESTROYER OF WORLDS" ever since. It's hard to reconcile the repressed murder memories, he totally gets it. They can talk.