The Scarlet Witch
Wanda Maximoff was born in Sokovia along with her twin brother Pietro as the orphaned children of a former cleaning woman turned freelance mercenary agent named Magda Eisenhardt. When they were ten, their adoptive parents, Django and Marya Maximoff, who were old friends of Magda before her passing, died themselves as a result of a bombing caused by several Stark Enterprise missiles stolen by HYDRA terrorists, and trapping the twins beneath a pile of rubble for several days until their rescue. The attack from then on caused them to foster a burning hatred toward Tony Stark due to their perceived belief of him being responsible for building the missiles in the first place. Years later, Wanda and Pietro volunteered to undergo experiments involving the Chitauri scepter, little realizing that they were now under the power of the same entity which caused their traumatic bombing in the first place, HYDRA. The scepter gave the twins newfound abilities which they later used in their vendetta against the Avengers and Baron Strucker. However, after learning that their second ally, Ultron, was planning to wipe out humanity, they escaped his subjugation and joined the Avengers to stop his diabolical plan once and for all.
Some time later, following the fallout of the Civil War, when she became a fugitive for siding with Cap against the Sokovia Accords, Wanda eventually found out that she and Pietro, who by this time had already been killed by Ultron, were actually the children of Magda... and the mutant overlord Magneto, and that all the Chitauri Scepter's energies had done was simply activate their latent mutant-gene powers. Following this revelation, Wanda chose to leave the Avengers in order to confront her father about their existence and why she and Pietro were abandoned so long ago.