Duke Orsino is a fictional character from William Shakespeare's play Twelfth Night, believed to have been written around 1600-1602.

Duke Orsino is a man with high romantic imagination and is a melancholy lover.

He finds himself becoming more and more fond of his new page boy, Cesario (Viola in disguise), the daughter of a nobleman who knew Duke Orsino.

Viola falls in love with Orsino, despite continuing to plead his case to Olivia.

Later, when Viola's twin brother Sebastian comes to Illyria, he is mistaken as Cesario by Olivia and is asked to marry her, to which he agrees.