One who dissembles; one who conceals his opinions or dispositions under a false appearance; a hypocrite. It is the weakest sort of politicians that are the greatest dissemblers. (Bacon) Priests, princes, women, no dissemblers here. (Pope)
a person is called a dissembler with reference to his concealment of his real character, and a hypocrite with reference to his assumption of a false character. But hypocrite is the stronger word, being commonly used to characterise a person who is habitually insincere and false, especially one who makes professions of goodness when his aims are selfish and his life corrupt.