IAGO: I am one, sir, that comes to tell you your daughter and the Moor are now making the beast with two backs.
William Shakespeare (1564-1616) English dramatist and poet
Othello, Act 1, sc. 1, l. 129ff (1.1.129-131) (1603)
(Source)
Speaking to Desdemona's father, the senator Brabantio. Earliest recorded use of "beast with two backs" in English; though Rabelais used it in Gargantua and Pantagruel (c. 1532), but that is not known to have been translated to English until the late 17th Century. (More info here).
