noun
who; what kind of person
Used to ask about someone's identity, often with a nuance of suspicion or curiosity about their true nature or background. Common in questions like 何者だ？ or 何者なんだ？
あの男は一体何者なんだ？
Who on earth is that man?
彼が何者かは誰も知らない。
Nobody knows who he is.