Dissembler
/dɪˈsemblər/
Definition 1 of 1
Pro Tip 1/3Hidden Intentions
Dissemblers may appear trustworthy, but covertly manipulate or deceive others. 
The spy was a dissembler, befriending others only to gather intelligence.
Pro Tip 2/3Negative Connotation
Using 'dissembler' suggests a lack of honesty and may imply criticism. 
Nobody trusted the politician because they considered him a dissembler at heart.
Pro Tip 3/3Faux Friendliness
A dissembler might act friendly for personal gain, not from genuine feeling. 
She played the dissembler, smiling at co-workers while plotting their downfall.