(a person or body being) unidentifiable (unidentified)
guarantor; surety; person responsible for another's behavior
identification; background check; identity confirmation
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)