10Mystique (X-Men Trilogy)
Before X-Men fans were reintroduced to a younger Raven Darkholme/Mystique in the form of Jennifer Lawrence in X-Men: First Class, Rebecca Romijn (previously known as Rebecca Romijn-Stamos) portrayed the deadly shape-shifting mutant in the original trilogy of films.
Uncompromising and fiercely devoted to the villain Magneto (Ian McKellan), the
first cinematic version of Mystique lacks any kind of backstory, making her all the more terrifying. Capable of impersonating anyone at all and able to perform gymnastic feats of mayhem, Mystique easily infiltrates the inner circle of anti-mutant Senator Kelly (Bruce Davison) killing his bodyguard and eventually taking his place - evidently, doubling as a United States senator is all part of the gig.
Mystique is essentially Magneto's fanaticism in action - at least in the original X-Men films. The quasi-reboot Days of Future Past presented a much more conflicted character, but her ruthless and exacting skills are still very much on display.