Wanda Maximoff, like her twin brother, is a mutant, with the ability to "hex" an opponent, triggering a "bad luck" effect. Years later, it was revealed her power was much greater, able to "warp reality" by tapping into actual magic. Wanda was married for a time to the android Avenger, the Vision. She has been an Avenger on and off as well, currently not on the team but a main character in the big event Avengers vs. X-Men.
