Because you like Mary Margaret Blanchard in Once Upon a Time

A crabby troll, Karkat Vantas is perpetually angry about his lot in life. See them in Homestuck.

A believer in the pursuit of justice, Garrus Vakarian hates it when bad guys slip through the cracks of the bureaucratic justice system. See them in Mass Effect.

Pro: Johan Liebert is handsome and charming. Con: he's also a sociopathic killer. See them in Monster (TV Show).