Twelfth Night, or What You Will is 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 the Countess Olivia. Upon meeting Viola, Countess Olivia falls in love with her thinking she is a man.
The Play is particularly provocative and interesting, since the role of its heroine, Viola, would have been played by a boy actor, who was cross-dressed as a female character, who cross-dresses as a boy. The story line has inspired plenty of remakes and adaptations, including the popular teen flick She's the Man, starring Amanda Bynes.
Today, Twelfth Night is one of the most popular and beloved of Shakespeare comedies perhaps because of its rebellious portrayal of gender ambiguity.