誰（だれ） is a substitute noun that is used in Japanese to describe unknown people. Due to Japanese particles behaving in very specific ways, 誰（だれ） will be translated differently depending on the particle that follows it.
誰（だれ）が・誰（だれ）で・誰（だれ）に・誰（だれ）を (who), 誰（だれ）の (whose), 誰（だれ）か (somebody), 誰（だれ）も (any/everybody).

• 誰（だれ）がくる？
  Who is coming?
• お前（まえ）は誰（だれ）で行（い）く？
  Who are you going with?
• これは誰（だれ）のノートですか。
  Whose notebook is this?
• 部屋（へや）に誰（だれ）かがいる。
  Somebody is in my room.
• これは誰（だれ）に送（おく）る？
  To whom are you going to send this?
• 誰（だれ）を連（つ）れて来（き）ますか？
  Who will you bring with you?
• 誰（だれ）も優（やさ）しいね。
  Everybody is nice, aren't they?