Wanda is the twin sister of Quicksilver and daughter of mutant supremacist Magneto, who took the twins away from their human mother and raised them within his Brotherhood of Mutants. The twins were always close, with Wanda generally deferring to Pietro in all things. While her brother bore the brunt of their father’s contempt for his children, Wanda was Pietro’s confidante, consoling him. After their father was reportedly killed in Washington, Wanda backed Pietro’s leadership of the Brotherhood. She helped him try to recover Magneto’s corpse from the military, only to discover it was absent. During the course of this mission, Cyclops tried to persuade them to join the X-Men. Wanda nearly convinced Pietro to do so, but the moment was lost when a soldier shot at her. Still, Wanda began to question their militant anti-human campaign. When the X-Men were abducted by Weapon X, the Brotherhood rescued them, Wanda used her powers to remove the neural implants that controlled the agency’s captives.

Under Quicksilver, the Brotherhood became less murderous. The twins also secretly agreed to assist S.H.I.E.L.D. black ops on selected missions in return for the release of mutant “political prisoners“, helping to repel a Chitauri invasion of Earth alongside the Ultimates. Magneto subsequently turned up alive, and took back the Brotherhood. Regarded as traitors by their fellow mutants, fearful of Magneto‘s retribution for Quicksilver‘s part in his earlier defeat, and branded by working with humans, the twins found sanctuary with S.H.I.E.L.D. Magneto, however, penetrated the agency’s Triskelion base and forced Wanda to watch as he shot her brother in the knees. Though Quicksilver recovered, their old ties were irrevocably severed, and they became full time members of the Ultimates.

Wanda is not above using her brother's devotion to her to manipulate him; when the Ultimates were trying to capture Thor, she spurred a badly injured Quicksilver back into action by lying, saying that Thor had hurt her, ultimately securing victory for the team. When the murdering mutant Longshot hid out in the Savage Land, where Wanda grew up, she tracked him down and used her own probability manipulation powers to override his. Since then she has tried to stop Emma Frost's mutant students from breaking into Triskelion to free one of their own, and assisted the Ultimates in disarming a Middle-Eastern country.