Pronoun case, subject and object pronouns, who versus whom on ACT English

A focused answer to pronoun case on ACT English: using subject pronouns (I, he, she, we, they, who) for subjects and object pronouns (me, him, her, us, them, whom) for objects, and the tricky cases of compound subjects and objects, comparisons with than or as, and who versus whom, with a drop-the-other-noun test.