a wolf in sheep's clothing
US /ə wʊlf ɪn ʃiːps ˈkloʊðɪŋ/
UK /ə wʊlf ɪn ʃiːps ˈkloʊðɪŋ/

1.
披着羊皮的狼
a person who appears friendly or harmless but is actually dangerous or malicious
:
•
Be careful of him; he's a wolf in sheep's clothing.
小心他;他是披着羊皮的狼。
•
The new manager seemed nice at first, but he turned out to be a wolf in sheep's clothing.
新经理一开始看起来很好,但他原来是披着羊皮的狼。