The relative pronoun WHO represents the subject in the clause.
Subject pronouns are I, you, he, she, it, we, they.
The relative pronoun WHOM represents the object in the clause.
Object pronouns are me, you, him, her, it, us, them.
The relative pronoun/adjective WHOSE represents the possessive adjective or possessive pronoun in the clause.
Possessive adjectives are my, your, his, her, its, our, their.
Possessive pronouns are mine, yours, his, hers, its, ours, theirs.