Because you like Madame Vastra in Doctor Who
Dolores Umbridge keeps her villainy hidden (albeit poorly) behind a sheen of sugary pink politeness. See them in Harry Potter Series.
Margaery Tyrell is one of the most adept and charming liars there is. See them in Game of Thrones.
Bobby Singer is a redneck ghost hunter, but all he wants to do is retire to the junk yards of South Dakota. See them in Supernatural.
Prideful and psychotic tendencies combine to make Dr. Eggman a dangerous and villain who will squash anyone in his path. See them in Sonic the Hedgehog.
Madman, murderer, or musician? No one knows the Phantom behind the mask. See them in The Phantom of the Opera.
A bloodsucker, Carlisle Cullen is actually more likely to give you a blood infusion. See them in Twilight.
There isn't a man in the world who executes his job with more finesse than Monsieur Gustave H. See them in The Grand Budapest Hotel.
There can be no doubt that Ben Linus is a huge liar. But one man's lies are another man's necessary steps to protect his people. See them in Lost.