A wolf in sheep’s clothing
Definition 1 of 1
Pro Tip 1/3Hidden Dangers
This phrase warns of deception. It suggests someone may hide malicious intentions behind a kind facade. 
He donated to charity, but he was a wolf in sheep's clothing, embezzling funds.
Pro Tip 2/3Figurative Speech
Remember, it's a metaphor. No actual wolf or clothing is involved; it's about contrasting appearances and reality. 
The politician was a wolf in sheep's clothing, with a friendly smile but corrupt motives.
Pro Tip 3/3Trust Carefully
Use this phrase to advise caution in judging people's character based solely on their outward behavior. 
I'd be careful around the new guy; he might be a wolf in sheep's clothing.