 McKern's most notable Shakespearean role was as Iago in "Othello", in 1952.In 1955 he appeared in "The Burnt Flower Bed" by Ugo Betti directed by Peter Hall at the Arts Theatre Club in London.He played Big Daddy in Peter Hall's production of "Cat on a Hot Tin Roof" at the Comedy Theatre in 1958 and went on to play the German ambassador in another Peter Hall production, "Brouhaha" starring Peter Sellers at the Aldwych Theatre.