Malvolio is Olivia’s deluded and much-mocked steward in Shakespeare’s Twelfth Night. The reference is to Act 3 Scene 4:
Where is Malvolio?
He's coming, madam; but in very strange manner. He
is, sure, possessed, madam.
Why, what's the matter? does he rave?
No. madam, he does nothing but smile: your
ladyship were best to have some guard about you, if
he come; for, sure, the man is tainted in's wits.