As Olivia's uncle, he lives in her household and thus is able to interact with the characters from the play's major plot. He marries Maria at the end of the play.
Although he possesses a festive personality, Sir Toby can be rather cruel in his pursuits of pleasure. In one instance, he befriends a silly squire named Sir Andrew Aguecheek but takes advantage of him financially and encourages him to court Olivia, a hopeless pursuit. Sir Toby is most cruel to Olivia's head steward Malvolio. With help from Maria, he makes Malvolio believe the lady Olivia wishes to marry him. Sir Toby carries this prank quite far, eventually imprisoning Malvolio in a dark room.