This is the 13328th most frequent Spanish word.
quien
"Who" or "whom."
In this sentence, 'quién' is used as an interrogative pronoun to ask about the identity of a person.
¿Quién es esa persona?
Who is that person?
Here, 'quien' serves as a relative pronoun to introduce a clause providing more information about the author.
El autor, quien escribió este libro, es muy famoso.
The author, who wrote this book, is very famous.
In this case, 'quien' is utilized as an indefinite pronoun to refer to an unspecified individual or group who meets the condition.