Viola / Cesario
Viola is the protagonist of the story, and is in actual fact two different characters - herself, a young woman who believes she is now all alone after a shipwreck that she thinks has killed her twin brother, and Cesario, a young man who has found work in the home of Orsino, with whom she is falling in love. Viola seems to be the catalyst for the key love triangle in the film. She loves Orsino, who thinks she is a boy and therefore does not consider her in a romantic way. Orsino loves Olivia, who has never treated him with anything other than total disdain. Olivia loves Cesario, and showers "him" with gifts in an attempt to win his love and his hand in marriage, unaware that "he" is actually "she".
Viola also engenders the ire of a couple of characters, principally Orsino, who, despite liking Cesario feels that he is making a play for Olivia, and feeling also that if it was not for this fact Olivia would notice him and reciprocate his love. As Cesario, Viola also upsets Antonio because as Cesario she does not recognize him, which gets him into trouble. He is upset because she looks exactly like her twin Sebastian whom Antonio is never apart from, and whom he feels has now betrayed him.
Viola's disguise is at first extremely clever because it gets her a job that she needs as she is now alone, it ultimately becomes a millstone around her neck because it prevents her from acting on her feelings for Orsino. She ultimately finds love at the end of the story when her identity as a young woman is revealed.
Orsino
Orsino is an Ilyrian nobleman who is in love with Olivia. She does not reciprocate his feelings and treats him disdainfully but this does not seem to resonate with him as a lack of interest and he attributes it to her being in mourning for her brother who has recently passed away. He takes an immediate liking to his new staff member Cesario whom he promotes to his own personal page boy. He also begins to feel resentful of Cesario whom he believes is making a play for Olivia. Once Cesario is shown to be Viola, Orsino falls in love with her and reciprocates her love. He also seems to find the fact she has dressed as a man attractive and titillating, adding to the sexual fluidity of the film.
Olivia
Olivia is a noblewoman from Illyria, and as rich as she is beautiful. She is also well aware of her beauty which makes her slightly less attractive. She has many suitors but since her brother has recently passed away she does not feel it proper to respond to their advances. As a noblewoman she is conscious that she needs to marry someone of similar social standing so that she does not lower her own "rank" or status in society. When she sees Cesario she is instantly smitten but her love seems generally shallow and easily switched from one person to another. It seems to be the chase that fulfills her more than the relationship. She is a woman who is used to getting her own way and this is evident in her courtship style; she showers the object of her affections with gifts and love tokens until she almost gifts them into submission. It is definitely a skin deep infatuation because finding that she has married Sebastian instead of Cesario does not seem to upset her, largely because they are identical in appearance.
Malvolio
Malvolio is the joke of the story, but the audience does not feel sorry for him because he has an obnoxious personality and grandiose ideas. He is not of noble birth but feels that it is entirely possible for Olivia to fall in love with him. This is impossible because not only is he not from the nobility, he is actually the chief steward of her household. He is not much fun and disapproves of everything that others find enjoyable. He is very ambitious and a social climber.
Sebastian
Sebastian is Viola's twin brother, and each of the siblings believes the other to have drowned after the shipwreck. He is close with Antonio and the two are rarely apart. His sexuality is a question mark, but he ultimately ends up married to Olivia, largely because she is beautiful and rich. He does not have his sister's personality but fulfills Olivia's visual requirements because he looks like "Cesario" with whom she is in love.
Sir Toby Belch
As his last name suggests, Sir Toby is a man of few social graces when he is sober, which is rarely, and he enjoys drinking ale. He is Olivia's uncle and he lives with her but he is an embarrassment to her because of his drunken behavior. He is an irritant to many at the house, particularly the humorless Malvolio, but does have an admirer in Olivia's lady-in-waiting, Maria, whom he ends up marrying. The two are great conspirators when it comes to pranking Malvolio, which is easy because he takes himself so seriously.
Maria
Maria is Olivia's lady-in-waiting and is clever, street-smart and wily. She very much enjoys the company of Sir Toby and manages to elevate her own status by marrying him. She is the brains behind the pranks that the two play on Malvolio, whom she does not like. Their mutual dislike is ironic because they both have the same goal - to rise above their given station - but Maria plays a much longer game than Malvolio which is why she is ultimately more successful.
Antonio
Antonio is the most gender-fluid character in the film. He is Sebastian's constant companion and we see that he is in love with his friend but unable to act on this. He is one of the characters in the play whose unrequited feelings of love remain unfulfilled at the end.
