Mystique is a member of Magnet's band of mutants. Mystique's mutant ability is shape shifting. Her base form is that of a blue, scaly skin. Somehow Rebecca Romijn still makes this form attractive.
Nightcrawler: Excuse me? They say you can imitate anybody, even their voice. Mystique: [as Nightcrawler] Even their voice. Nightcrawler: Then why not stay in disguise all the time? You know, look like everyone else. Mystique: Because we shouldn't have to.