Although wolves are sometimes portrayed favorably in the Bible (especially in the visions of Isaiah in chapters 11 and 65), overall they are not among the Biblical writers’ favorite animals—especially when compared to their typical prey, sheep. A colorful combination of these two creatures appears at Matthew 7:15, where the King James Version reads “Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves.”
From this passage comes the expression “a wolf in sheep’s clothing,” which usually describes someone who hides malevolent intent under a cloak or façade of kindness. Writers in the popular press employ this imagery in a seemingly infinite variety of contexts, but not always with the precise meaning applied to false prophecy by the author of the Gospel of Matthew.
When applied to cars—which is a surprisingly popular usage—the phrase has a more positive connotation (as reported in a feature titled “Take Off Like a Bat Out of Hall” from the Sydney Morning Herald): “The BMW M3 is best described as a car that fits that old saying: a wolf in sheep’s clothing. But only if good things can be said about the wolf!”