Which Shakespeare comedy includes the characters Viola, Orsino, and Malvolio?

The Shakespeare comedy featuring Viola, Orsino, and Malvolio is Twelfth Night.

Viola is shipwrecked on the coast of Illyria and disguises herself as a young man named Cesario. She enters the service of Duke Orsino, who is pursuing Olivia. The disguise creates a love triangle: Viola loves Orsino, Orsino loves Olivia, and Olivia falls in love with Cesario.

Malvolio, Olivia's steward, supplies a separate comic storyline. After he is tricked by a forged letter, he behaves as though Olivia loves him, wearing yellow stockings and smiling constantly. His self-importance makes him an object of ridicule, though his humiliating treatment also gives the play a darker edge.

The title refers to the twelfth night after Christmas, traditionally associated with festivities and role reversals. A frequent mistake is to confuse the play with A Midsummer Night's Dream, another Shakespeare comedy involving mistaken identities and romantic confusion; Viola, Orsino, and Malvolio belong specifically to Twelfth Night.