Fig.: it refers to someone apparently nice and harmless, but dangerous in reality

Everybody thought he was a wonderful person until it was discovered that he made his living by defrauding the elderly. Your typical example of a wolf in sheep's clothing!

Per tutti era una brava persona, poi si è rivelato un lupo in veste d'agnello quando si è scoperto che viveva truffando anziani

 If I were you, I wouldn't trust him. I'm afraid he's a wolf in sheep's clothing: nice outside but vicious inside

Se fossi in te, non mi fiderei di lui. Ho paura che sia un lupo in veste d'agnello: bello fuori, ma brutto dentro

I do have a few doubts about this new “team member”. For me he's a bit like a wolf in sheep's clothing as he presented himself as a liberal to gain the President's favor, but worked behind the scenes to hold back some of the reforms

Ho delle riserve su questo “collaboratore”. Per me è un po’ un lupo travestito da agnello perché si è venduto come progressista per ottenere i favori del Presidente, ma ha lavorato dietro le quinte per intralciare alcune delle riforme

The defendant was confident, but a skilled prosecutor could have easily proven to the jury that there was a wolf in sheep's clothing hiding beneath the tweed suits of a high school teacher

L’imputato era sicuro di sé, ma un buon procuratore sarebbe riuscito a convincere la giuria che, con i suoi completi di tweed da insegnante delle superiori, era in realtà un lupo travestito da agnello

In the Sermon on the Mount (Gospel of Matthew 7:15-16, King James Version), Jesus says to his followers: Beware of false prophets, which come to you in sheep's clothing, but inwardly they are ravening wolves. By their fruits shall ye know them