In Shakespeare's Twelfth Night, we see how Viola (disguised as a man under the name of Cesario) becomes a page for Duke Orsino. The Duke pursues Countess Olivia romantically, for which he assigns Orsino/Viola to carry his love messages to her and convince Olivia to marry the Duke. In the process, Orsino/Viola falls in love with the Duke, and Olivia falls in love with Orsino/Viola whom she thinks of as a man. When Sebastian turns up (who believes his sister to have drowned on the shipwreck) , alive and kicking, the whole town is talking about how they are identical. Before we know of any further events, we know that two identical people in one town, one of them involved in a love triangle, will create a series of mix-ups and mistaken identities between Viola and Sebastian.