who

A person under discussion; a question of which person.

(interrogative) What person or people; which person or people; asks for the identity of someone. (used in a direct or indirect question)

“I don't know who it is. (indirect question)”

(interrogative) What is one's position; asks whether someone deserves to say or do something.

“I don't like what you did, but who am I to criticize you? I've done worse.”

(relative) The person or people that.

(relative) Whoever, he who, they who.

“It was a nice man who helped us.”