Moira MacTaggert

While she did cameo in Last Stand, Moira MacTaggert is best known for her appearance in X-Men: First Class (portrayed by Rose Byrne), the CIA agent who discovered the existence of mutants and who helped Charles Xavier bring down the Hellfire Club. After Magneto took over as the leader of the Hellfire Club and after the agencies became aware of the existence of mutants, Professor X erased her mind in order to protect his school for gifted youngsters, as well as herself.

There is no knowing what happened to her afterwards, since she isn’t present during Days of Future Past. However, the X-Men: Apocalypse trailer shows her working once again with Professor X. Does this mean that her memories weren’t erased completely? This is least likely – instead, we believe that she continued pursuing her obsession of finding out all there is to know about the mutants.

And she has an active role in the fight against Apocalypse, since the trailer shows her costumed alongside the X-Men.