* Pronoun: This is the most common use of "who." It acts as a subject pronoun, replacing a noun that is the subject of a verb.
* Example: Who is going to the party? (Here, "who" is the subject of the verb "is going.")
* Interrogative Pronoun: This is the function of "who" when used to ask a question.
* Example: Who did you call? (Here, "who" is asking for the identity of the person called.)
* Relative Pronoun: This is used to connect a subordinate clause to a main clause.
* Example: I know the girl who won the contest. (Here, "who" connects the clause "who won the contest" to the main clause "I know the girl.")
So, the part of speech "who" is depends on its use in the sentence.