It's someone who tends to be a nice person but hides something or there is something off about him. Sometimes, you meet this kind of people and you know that his/her kindness hides a darker side.
I thought about sly or shady but they seem a bit too much, however I might be wrong. Is deceitful the correct term or is there a more specific one?
"I don't like the new boss, his kindness hides something"
" I don't like the new boss, he is _____"