In spoken English it is normal to use object pronouns such as me, him, her, or them after ‘as’ or ‘than’: I can’t run as fast as them. ♦ Henry’s older than me. A subject pronoun such as I, he, she, or they is rarely used by itself after ‘as’ or ‘than’, except in very formal English: ♦ Henry is taller than I.
Object pronouns are also normally used after the verb ‘to be’ in spoken English: ‘Who’s there?’ ‘It’s me.’ ♦ I knew it was him. Some people think it is more correct to use subject pronouns after ‘to be’, but this sounds very formal and old-fashioned: ♦ It is I. ♦ I knew it was he.
In writing, subject pronouns are more often used after the verb ‘to be’, especially if there is a following relative clause: It was he who first suggested the idea.