(a person or body being) unidentifiable (unidentified)
 identification;  background check;  identity confirmation
 guarantor;  surety;  person responsible for another's behavior
 identity or background check (often to see if someone is a burakumin)
 (personal) guarantor;  (personal) surety;  person providing a character reference
 John Doe;  Jane Doe;  person unknown
 personal reference letter;  personal reference guarantee
 reference (e.g. on CV, resume)