With nouns and pronouns, you’re likely to observe an inequality: pronouns come in nine flavors, but nouns have only four. Why? Because nouns change form only to become plural or possessive, whereas pronouns change to become personal, possessive, reflexive, intensive, demonstrative, and so on, all in the singular and plural.
Check it out. Regardless of the role it plays, a noun remains fairly constant:
Personal: Sally drives a truck.
Possessive: Sally’s truck barreled past the exit.
Reflexive: Sally drove Sally to the depot. (Now you know why we have reflexive pronouns.)
Interrogative: Sally drove to the depot?
You get the idea. Now observe how versatile a pronoun is, changing form based on the role it plays:
Personal: She drives a truck.
Possessive: Her truck barreled past the exit.
Reflexive: Sally drove herself to the depot.
Interrogative: Who drove to the depot?