What is the role and dramatic significance of Maria in the Twelfth Night?

Maria is 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.