word usage - On the singular vs plural aspects of "who"

In a question like this one, for example,

Who have/has come?

Is the word "who" singular or plural? Or is it both plural and singular?

I have heard it’s plural. Please correct me if I am wrong.

Answer

Who can be either an interrogative pronoun ("Who is that?") or a relative pronoun ("The man who sells fruit"). Neither interrogative pronouns (question words) nor relative pronouns (which/that/who and variations) are bound to grammatical number by themselves. The plurality is instead bound to the object in question.

Examples:

"Who is that man?" - singular due to "man"

"Who are those people?" - plural due to "people"

"The man, who is sitting there,..." - again singular due to "man"

"The men, who are sitting there,..." - plural due to "men"