From a Wall Street Journal story by Jeanine Basinger headlined “A Match Made in Hollywood”:

Hollywood is famous for successfully pairing acting couples, some “married” on screen (Greer Garson and Walter Pidgeon), some musical (Fred Astaire and Ginger Rogers), and some who became involved both off-screen and on (Katharine Hepburn and Spencer Tracy). The gold standard of the on-screen romance that becomes an off-screen love affair is the one that contains a good lesson on how to whistle: Humphrey Bogart and Lauren Bacall, who first starred together in “To Have and Have Not.”