The traditional grammar rule states when a pronoun follows a linking verb, such as "is," the pronoun should be in the subject case. It’s also called the “nominative.” That means it is correct to say, “It is I,” and “It was he who dropped the phone in shock when Jodie answered, 'This is she,'” because "he" is the same type of pronoun as "I.".
Yes, I'm serious, and that is the traditional rule, but fortunately most grammarians forgive you for not following the rule. In her aptly titled book Woe Is I, Patricia O'Connor notes that almost everyone says, “It is me,” and that the “It is I” construction is almost extinct