Why do these phrases contain a pronoun case for "who" and "whom?"
"Who was the star of last year’s award-winning movie?",
"To whom should we send the letter of commendation?", and
"Jon Bon Jovi, who is a well-known singer and actor, also owns an arena football team."
Who is used as a nominative case pronoun ( subjects and predicate nominatives)
Whom is used as an objective case pronoun. ( objects, direct and indirect and objects of prepositions)