Emma Frost was Charles Xavier's adopted sister who had the mutant power of telepathy and diamond form transformation. All her life she hated her mutant powers and tried to hide them away from the world, but it took a bit of coaching from Erik Lensherr and Sebastian Shaw to make her embrace her true self, siding with them as the confident White Queen to help form the Brotherhood of Mutants, even going so far as to turn against Charles on the basis that he was too soft on humanity's opinion on mutantkind. However, she broke away from the team when Magneto began to take their mutant pride agenda too far by sending Mystique, a fellow mutant whom she formed a sisterly bond with, to kill Bolivar Trask when the dwarf scientist created the Sentinel Program to hunt down mutants. She hid away from the world from then on for many years until realizing, upon the year 2023 when the malevolent A.I. Ultron returned from the Infinity War debacle to take control over the dormant project and use them to conquer the world, that things needed to be changed drastically for the better, sending a mental message to Charles to help patch up their relationship in the past and stop Magneto & his forces, Mystique included, from killing Trask in 1973.
In the end, thanks to the help of the time-travellers Kitty Pryde and Wolverine, Magneto & Mystique were defeated and Trask saved from assassination, all the while Emma began taking up a much more active role in protecting mutantkind, eventually rebonding her familial relationship with Charles to save him and his band of new recruits 10 years later in 1983 when the threat of Apocalypse arrived to ruin everything they all worked so hard to save. Now as a maternal old woman in her late 60's to early 70's, she serves as one of the directing members of the X-Men, helping to usher in a new era of pacific coexistence between humans and mutants. As for Mystique, she's kept a low profile, having willingly depowered herself to get away from the hectic lifestyle she lived in the past.