I follow him to serve my turn upon him:
We cannot all be masters, nor all masters
Cannot be truly follow’d.

– William Shakespeare

Othello, Act 1, Scene 1. Shakespeare’s most terrifying villain Iago reveals to Roderigo that he is serving Othello only to serve himself. He is Othello’s ensign or standard-bearer who wants to be promoted to lieutenant but has been passed over. Iago hides behind a mask of loyalty and friendship for Othello, while secretly plotting his ruin.