Orsino, Duke or Count of Illyria
Though his title in the play is disputed, Orsino is the ruler of Illyria, with some naval experience behind him. He is lovesick for the Lady Olivia, who will not return his affections; Viola is taken into his service, as the boy Cesario, and is quickly taken into his confidence and tries to woo Olivia for him. However, Orsino's affections shift by the end of the play; he drops his self-indulgent behavior, and develops affection for Viola.
Curio, Valentine
Two of Orsino's attendants. Valentine is sent to try and woo Olivia, though he is not quite as successful at gaining entrance to Olivia's house as "Cesario" is. Curio accompanies Orsino on his visit to Olivia's in the last act, though he says nothing; their basic purpose is to wait on Orsino as best they can, but they are not as close to him or as important in the action as Viola is.
First Officer, Second Officer
These two recognize Antonio as having committed crimes against Orsino, and arrest him. In the last act, they hold Antonio, as they remind Orsino of the crime that Antonio had committed.
Viola
A young woman who is shipwrecked, having lost her twin brother Sebastian, and lands in Illyria quite by accident; she resolves to make the best of her situation, and be taken into Orsino's service, as a young eunuch named Cesario. Viola is quickly taken into Orsino's confidence, and he tells her all the secrets of his heart; she is entrusted with wooing Olivia, though Olivia herself falls for Viola as Cesario. Viola herself is in love with Orsino, though she cannot admit this; she does succeed in gaining Orsino's affections, however, and gets him to be a more honest, less self-centered person.
A Sea-Captain
He rescues Viola from drowning, and helps her transform herself into Cesario and become Orsino's page. Later, he has supposedly had some issues with Malvolio somehow, and must be found so that Viola may reclaim her female clothes and possessions.
Sebastian
Viola's non-identical twin brother, who nevertheless bears a great resemblance to her. Viola tries to imitate her brother in her disguise as Cesario, as the two are mistaken for each other in many scenes. Sebastian himself is saved by Antonio, and the two become fast friends. Quite by accident, Sebastian comes across Olivia, and is taken for Cesario; she proposes, and they are quickly married, despite Sebastian not knowing who she is.
Antonio
Another sea-captain; he saves Sebastian's life, and appears to be benevolent in his intentions toward Sebastian. However, he has a questionable past, and was involved in some doings at sea that mean he is wanted by Orsino. He stops a duel between Viola and Sir Andrew, mistaking Viola for her brother Sebastian. His relationship with Sebastian has argued to be a little more than friendlythough this can certainly be disputed.
Olivia
A noblewoman, Countess of Illyria. She lost her father, then her brother right before the beginning of the play; she resolves to be in mourning for her brother for seven years, thus thwarting Orsino's attempts to woo her. She becomes enamoured of Viola, who acts as a messenger for Orsino; and though Olivia tries her best to win Viola, Viola does her best to let her down easily, because Viola is not a boy like she pretends to be. Olivia rushes off and marries Sebastian, thinking that he is Viola as Cesario; but everything works out in the end.
Maria
Olivia's gentlewoman-maid, a witty, wily woman who has some affection for Sir Toby. It is she who resolves to get revenge on Malvolio, after he embarrasses the party; she claims to have handwriting like Olivia's, and will use that gift to trick Malvolio. She is actually a good-natured woman, though she loves a good joke, and holds her own with the "boys"Sir Toby, Sir Andrew, and Feste.
Sir Toby
Surname Belch, not very complimentarybut sadly, accurate. He is Olivia's ill-behaved uncle, and spends most of his time drinking, fooling, and carousing with Sir Andrew. He takes part in the pranks against Malvolio, and arranges the duel between Sir Andrew and Viola as well. He is hot-tempered, and usually unruly, but not a bad fellow either.
Sir Andrew
Surname Aguecheek, also not complimentary, but correctly describing his thin, pale face. He is a complete, very dense fool, who can't help but misconstrue every word his friend Sir Toby says. He hopes to win Olivia's affection, though they have few interactions in the play. Jealous of the attention that Olivia pays to "Cesario," he challenges the young man to a duel, that is never quite completed.
Malvolio
Olivia's steward, a man who is supposedly good at his job, but is stern and hates merrymaking. He rebukes Sir Toby and company very harshly, for which they resolve to get revenge. They play on his vanity and his pride by convincing him that Olivia loves him, and getting him to act foolish in front of her. He is finally locked up in a dark place, and tormented by Feste; in the last act, he comes forward and tells of his ordeal, and swears revenge on everyone involved, having not learned any lessons.
Fabian
A member of Olivia's household with responsibilities that are never explained. He is a sort of mid-play replacement for Feste, taking part in the plots against Malvolio with Sir Toby and Sir Andrew. He doesn't seem to have much of a personality, but is included in the play for the purpose of expositionand he is also good at stating the obvious for the audience.
Feste
A jester and musician who lends his services to Olivia, and to Orsino as well. Feste is quick-witted and quite skilled at wordplay; but he is also somewhat cruel, as seen in his behavior toward Malvolio. Feste may act the part of the fool, but in fact he is very wise and perceptive about people's natures; he knows the perfect song for any occasion, but resents when his services are taken for granted.
A Priest
Marries Sebastian and Olivia, and later testifies about this union to Orsino and others.
