From More Intelligent Life:

He’s one of the great villains. But why exactly does he destroy Othello? As the RSC casts a black Iago, Irving Wardle 
(first half) and Robert Butler (second half) pick nine of the best readings of the role.

Iago1964 FRANK FINLAY, National Theatre
Olivier took care that his Othello should not be overshadowed by giving the part of Iago to Frank Finlay (below left)—who duly sank to the occasion as a plodding squaddie, in lowly contrast to his glamorous general. Olivier, however, always at his best in physical contact, granted that privilege to his unsavoury underling, who seized the opportunity to cling round his neck like an incubus pouring poison in his ear. As a character, his motive was erotic; as an actor, it was self-preservation. In these scenes, Olivier was not the boss.

1976 TIMOTHY WEST, Nottingham Playhouse
Taking advantage of Daniel Massey’s flyweight Othello, Timothy West used every trick in Iago’s repertoire to push the play towards farce. The most plain-dealing character on stage, he enlisted the audience as conniving accomplices in the farcical pleasure of knocking a big shot off his plinth. Forget plot motive; the show’s mainspring was that we are all Iagos.

More here.