Who is the nominative pronoun. It has two uses:
- It’s the subject of a verb—e.g., Who gave you that book?
- It’s a predicate nominative—e.g., This is who I am.
Whom is an objective pronoun. It also has two uses:
- It is the object of a verb—e.g., Whom should I call?
- It is the object of a preposition—e.g., From whom did you get this information?
