1. used to ask about the identity of a person or people
Usage: interrogative
2. used to introduce a clause that gives more information about a person or people previously mentioned
Usage: relative

Examples

• Who is at the door?
• Who called you last night?
• The woman who lives next door is a teacher.
• I know someone who can help you.
• Who wants to go to the movies?
• The students who studied hard passed the exam.
• Who told you that story?