Who vs Whom vs Whose
Pronoun: Who - Subjective, Objective and Possessive Forms

The Pronoun Who

The pronoun who, in the English Grammar, is the interrogative and relative Pronoun, used to refer to humans. wikipedia

Other pronouns in these groups ( which, that, what, whatever, whichever, etc) do not change forms across case, person, gender, and number, but who does change form with case.

• who - Nominative / Subjective
  • Who took my car?
  • I want to know who did that.
• whom - Objective
  • With whom are we meeting?
  • To whom do you wish to speak?
• whose - Possessive
  • Whose car is it?
  • I forgot whose phone it was.