is who a pronoun

Yes, "who" is a pronoun.

Explanation:

• "Who" is an interrogative pronoun when used to ask questions about a person.
  Example: Who is coming to the party?

• It can also function as a relative pronoun to introduce a relative clause referring to people.
  Example: The person who called you is my friend.

So, "who" is indeed a pronoun used primarily to refer to people.