A wolf in sheep's clothing is one who appears to be friendly but is really an enemy, a dangerous person who pretends to be quite harmless. The allusion here is to the fable of Aesop. A Wolf in a Lamb's Skin. A wolf once disguised himself in sheep's skin and succeeded in entering sheepfold. Soon a shepherd came to the fold to get the fattest sheep in the flock. In touching fold to see which was the best, he found an animal with hairy ears and woolly back. The shepherd put a rope round his neck and hung the animal high up on a tree.