1. Maria
1.1. The handmaid/servant of Olivia.
1.1.1. Maria plays an important part for the comedic setup of the play. Her handwriting convices Malvolio that Olivia loves her through forged love letters, setting up a hilarious sequence of events that involve Malvolio speaking in strange ways and even being locked away by a "priest."
2. Malvolio
2.1. The head butler of Olivia's household. Secretly wishes to be an aristocrat, and views himself as one. Thinks he has a chance from the fake letters.
2.1.1. Malvolio is a bit of a strange character. This is due to his seriousness and unwillful demeanor towards people of whom he is the butler to. His strangeness only gets stranger, as he is convinced that Olivia loves him and makes desparate attempts to prove he holds the same feelings.
3. Sir Tony Belch
3.1. The uncle of Olivia. Doesn't understand her grief.
3.1.1. Sir Toby sets up a large portion of the plot in the play. He sets up the battles for the rights to marry his niece, although these "rights" are eventually outruled by Olivia herself. He is also a large comedic factor by being a funny, belligerent drunk in scenes that prove some intensity.
4. Sir Andrew Aguecheek
4.1. The best friend of Sir Toby Belch.
4.1.1. Sir Andrew wants to marry Olivia in order to obtain more financial wealth, but fails to do so. He fights "Cesario" in order to woo Olivia, but Olivia's love is made out to Sebastian who marries her per his "manly obligation."
5. Fool/Feste
5.1. The court's jester. He mainly serves as a form of entertainment, but is wise with knowledge and with women.
5.1.1. The fool is wise and also has the greatest wits of the play. It is absolutely stunning how he is able to go from a position of lowliness and of such disrespect to a level of power. He sings all throughout the play, and makes a convincing attempt of driving Malvolio to insanity through his own desire of aristocracy.
6. Viola/Cesario
6.1. Has shipwrecked in Illyria, and is working under Orsino in disguise as a male to eventually marry him.
6.1.1. Viola is the ultimate tie-in between characters throughout the play. Not only does she have ties through Orsino's court and through Olivia hence her being a sort of messenger between her, her relatives, friends of her relatives, and Orsino, but her bond with Sebastian as a twin helps to somehow relate each character to each other in some way or another.
7. Olivia
7.1. She is currently greiving the death of her brother and refuses to reveal any part of herself for 7 years.
7.1.1. Olivia ultimately falls in love with "Cesario," but "he" does not have the same feelings of love that Olivia holds. Viola, in disguise, makes many attempt at trying to convince her that she needs to be the wife of Orsino, but all are to no avail. Eventually, she will break up the fight between many for her love, of which from this fight, she chooses Sebastian to be the one that she will marry.
8. Sebastian
8.1. The twin brother of Viola, has been shipwrecked and believes his sister to be dead.
8.1.1. Sebastian will enter into Orsino's court, of where he will then get greatly confused for his twin sister's disguise, Cesario. When he is entered into the play, everything seems to become chaotic, as his appearance at the house of the Countess ties both him and Viola in a similar conflict.
9. Antonio
9.1. Persisted against Sebastian's wishes to follow him on his journey.
9.1.1. Antonio eventually gets arrested by the guards of Illyria as he is recognized as an enemy of Orsino. He experiences betrayal, as he believes that Viola is Sebastian, and as Viola claims she has no clue who he is, Antonio practically goes mad. Antonio will run back into Sebastian, of which he then is one of the first to realize that he has somehow duplicated. By the end of the story, he is ultimately forgiven and attends the marriage ceremony at the end of the play.
10. Orsino
10.1. The duke of Illyria. He is madly in love with Olivia, but is unable to get her love.
10.1.1. Orsino throughout the play mainly tries to win over the affection of the Lady Olivia. He doesn't make much of an appearance in Act 3, but once he realizes the true identity of Viola, what she has told him in the past makes him remember that she had given subtle hints about her true gender.
11. Fabian
11.1. A servant of the Lady Olivia, who joins in on the pranking of Malvolio.
11.1.1. Although he never speaks often, Fabian plays a part in the development of the plot that includes the conflict for the affection for the love of the lady.