Charles Montagu Slater (23 September 1902 – 19 December 1956) was an English poet, novelist, playwright and librettist.Slater, born in Millom, Cumberland, was selected by Benjamin Britten as librettist for his opera Peter Grimes, which was based on "Letter XXII: Peter Grimes" in George Crabbe's poem The Borough.For the libretto, Slater eschewed the traditional five-stress line form of English rhyming or blank verse in favour of a more modern and conversational four stress line with rhyming couplets.