Feste, the Clown, has his character traits established by other characters comments, action and dialogue from his first entrance in Act I, scene v. He and Maria enter and she is admonishing him for being absent too long from Olivia's court. Maria's admonitions reveal that Feste relies upon his fool's wit to save him from trouble ("those
that are fools, let them use their talents"). This is emphasized later when Olivia approaches. He says as an aside:
Wit, an't be thy will, put me into good fooling!
Those wits, that think they have thee, do very oft
prove fools; ...'Better a witty fool, than a foolish wit.'
His action of absenting himself when it could risk Olivia's displeasure and lead to being dismissed from court shows he is willing to act out of independence and take risks:
MARIA: [My] lady will hang thee for thy absence.
Clown: Let her hang me: he that is well hanged in this
world needs to fear no colours.
This is an important trait as it helps prepare for and explain his bad behavior in the vicious trick played against Malvolio.
The dialogues he engages in with Maria and Olivia show that he is quick to turn a phrase to double meaning, as when he answers Olivia's pronouncement that he is "a dry fool" (i.e., no longer amusing) with the words: "for give the dry fool drink, then is the fool not dry." His dialogue with Malvolio shows that not everyone is a fan of the Clown's commission to deliver clownish wit, though Olivia defends the Clown's rights as court jester to reveal distasteful truth through foolery:
Oh, you are sick of self-love, Malvolio, and taste
with a distempered appetite. To be generous,
guiltless and of free disposition, is to take those
things for bird-bolts that you deem cannon-bullets:
there is no slander in an allowed fool, though he do
nothing but rail;
In addition, Feste's dialogue with Olivia and Malvolio helps set up the upcoming wicked prank against the vain Malvolio who is struck "sick of self-love."