A stock character can be considered a stereotype, and in drama, a playwright employs stock characters to further the complications of the story. Stock characters are used especially often in Comedies, as it is the recognizably stereotypical human foibles that make for good comic characters and situations -- foibles like craftiness, dimwittedness, miserliness, and being crazy-in-love or a braggart.
Maria is an embodiment of the "crafty servant" stock character. This character was found in Comedies of ancient Rome, but more contemporaneously to Shakespeare, the Commedia dell' Arte of Italy. This comic and improvisational theatre form allowed both male and female performers onstage and might have been a very strong influence on Shakespeare's theatrical sensibilities. The comic servant from Commedia who can be associated with Maria is Colombina, the crafty servant of the female lead of a play, a servant who also often had a love interest.
For more on stock characters, Commedia, and Maria, please follow the links below.
honestly that was so confusing it didn't really help me lol...
"A stock character is one that is a recurring character that is recycled in many plays, such as a ladies' maid, as is Maria in Shakespeare's Twelfth Night. Such a character would be likely to show up in any play that dealt with interaction between the upper and lower classes. What makes Maria different, however, is the fact that her personality and actions are anything but those of a stock character. She is vital to the plot, as it is her wit and intelligence that hatch the plot against Malvolio. She is far smarter than her companions, Sir Andrew and Sir Toby, and she is clever enough to pull off a complicated scheme. She is educated enough to forge her lady's handwriting and style well enough to fool Malvolio, who thinks he is her better. And, she is fearless and no-nonsense enough to deal with both the upper and lower class characters in the play in any situation."