何者 (nanimono) means “what kind of person”

More examples

新しく来た先生が何者なのか、まだ分かりません。atara shi ku ki ta sen sei ga nani mono na no ka ma da wa ka ri ma se n

We still do not know what kind of person the new teacher is.

Frames a person as an unknown figure whose identity or character is being questioned.

誰dare: A word used to ask which person is being identified.
どなたdonata: A polite word used to ask which person is being identified.

どのような人物であるかを問い、またはその人物の正体を指していう語。do no yō na jin butsu de a ru ka o to i ma ta wa so no jin butsu no shō tai o sa shi te i u go

何 (nani, "what") and 者 (mono, "person") combine to form 何者 (nanimono), asking what sort of person someone is and extending to who someone is.

In conversation, 何者 (nanimono) can sound more probing than a neutral question about identity, suggesting curiosity about a person's character or background.