He's mad that trusts in the tameness of a wolf
Fool:
"He's mad that trusts in the tameness of a wolf, a horse's health,
a boy's love, or a whore's oath."
The fool in Shakespeare's plays often serves as the person who sees things in the most honest way. In King Lear, his jester has been delivering stinging lines that get to the bottom of the truth, the most obvious being how King Lear gave away his kingdom to ungrateful daughters who have now demeaned and humiliated him. Lear has run out into a raging storm, wandering wildly and naked on the heath, sinking into madness over the ingratitude of his children. He is pulled at last into a farmhouse where his fool, the only person allowed to be frank with King Lear, continues to chide him about his character.