Twelfth Night, or What You Will is a romantic comedy by William Shakespeare, believed to have been written around 1601–1602 as a Twelfth Night's entertainment for the close of the Christmas season. The play centres on the twins Viola and Sebastian, who are separated in a shipwreck. Viola (who is disguised as Cesario) falls in love with Duke Orsino, who in turn is in love with Countess Olivia. Upon meeting Viola, Countess Olivia falls in love with her thinking she is a man.