a wolf in sheep's clothing

A person or thing that appears harmless but is actually dangerous or bad. Don't trust Dana—she's a wolf in sheep's clothing who will try to steal your position if given the chance. The politician portrayed himself as moderate, but turned out to be a wolf in sheep's clothing with a radical agenda.

Fig. a dangerous person pretending to be harmless. Carla thought the handsome stranger was gentle and kind, but Susan suspected he was a wolf in sheep's clothing. Mimi: Why shouldn't I go out with David? He's the nicest man I've ever met. Alan: He's a wolf in sheep's clothing, Mimi. Can't you tell?

An enemy disguised as a friend, as in Dan was a wolf in sheep's clothing, pretending to help but all the while spying for our competitors . This term comes from the ancient fable about a wolf that dresses up in the skin of a sheep and sneaks up on a flock. This fable has given rise to a rich history of allusions as in the Sermon on the Mount when Jesus speaks of false prophets in sheep's clothing, "but inwardly they are ravening wolves" (Matthew 7:15).

A wolf in sheep's clothing is someone or something that appears harmless or ordinary but is in fact very dangerous or powerful. The judge said Granger appeared to be a nice young gentleman, but was in fact a wolf in sheep's clothing — a ruthless individual with absolutely no morals. This car has to be the ultimate wolf in sheep's clothing. It looks like an ever-so sensible estate — until you hit the accelerator. Note: Less often, people describe someone as a sheep in wolf's clothing, meaning that a person seems dangerous or powerful, but in fact is harmless or ordinary. She was tall, with a loud voice and could seem a little intimidating but was in fact a sheep in wolf's clothing, loved by all who knew her. Note: In one of Aesop's fables, a wolf wraps itself in a fleece and manages to get into a sheepfold without being noticed. It then attacks the sheep and eats them. This image is also used in the Bible: `Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves.' (Matthew 7:15)

One who feigns congeniality while actually holding malevolent intentions.

An enemy masquerading as a friend. The term comes from Aesop’s fable about a wolf dressing up as a shepherd (in some versions, as a sheep) and sneaking up on the flock. In the Bible, Jesus warns of “false prophets which come to you in sheep’s clothing but inwardly they are ravening wolves” (Matthew 7:15). The expression has appealed to hundreds of writers. Clare Boothe Luce (Kiss the Boys Good-bye, 1939) used it to describe a predatory male collegian: “A wolf with a sheepskin.”