He dressed Jim up in King Lear’s outfit – it was a long curtain-calico gown, and a white horse-hair wig and whiskers; and then he took his theater paint and painted Jim’s face and hands and ears and neck all over a dead, dull, solid blue, like a man that’s been drownded nine days. Blamed if he warn’t the horriblest looking outrage I ever see. Then the duke took and wrote out a sign on a shingle so:

Sick Arab – but harmless when not out of his head.

And he nailed that shingle to a lath, and stood the lath up four or five foot in front of the wigwam. Jim was satisfied.

– Mark Twain

The Adventures of Huckleberry Finn, Chapter 24. To avoid Jim having to be tied up on the raft every day (pretending to be a runaway slave), the Duke figures out a better solution. He paints Jim in blue and makes him wear a King Lear costume. Jim spends the rest of the river journey looking undignified and like a sick Arab. The passage is an allusion to the protagonist of Shakespeare’s tragedy King Lear, who has episodes of madness.