Who (Someone / Anyone / No One)

Someone you do not know rings the doorbell, calls, or walks up at a reception desk, and you need to ask who they are.

どなた～ vs だれ～: Use どなた: どなたですか is the polite way to ask a stranger, a customer or anyone above you who they are. だれ means exactly the same, but だれですか to a caller sounds blunt, as if you were talking to a child. Keep だれ for friends, family, and questions about a third person in casual talk.

Saying nobody came, nobody knows, nobody is there.

だれも～ません vs だれか〜　/　だれでも～: Use だれも with a NEGATIVE verb: だれも来ませんでした. The particle decides the meaning: か makes 'someone' (だれか来ました, someone came), でも makes 'anyone at all' with an affirmative (だれでもできます), and も with a negative makes 'no one'. だれも with an affirmative verb is not 'everyone'; say みんな for that.