Wanda Maximoff (aka, Scarlet Witch) is a superhero in the fictional Marvel universe, who was created in 1964 and has been one of it's main superheroes, a B-list hero with a few comic book series.
The Scarlet Witch is one of the most powerful beings on Earth, able to alter reality on a global scale but is someone who is prone to mental breakdowns due to her mental illness, though usually it's under control. She has been a member of the Avengers superhero team for decades, and for a long time believed that she was a mutant who was the daughter of Magneto.
In reality she is a mutate who was engineered and her magical powers were amplified by Chthon, one of the Old Ones. Chthon has manipulated her several times and on occasion has been able to possess her, until her teammates break his control over her.