Cassandra Nova

Cassandra Nova is Charles Xavier's twin sister — a mummudrai, a parasitic entity from the astral plane that mimicked his DNA in the womb. Rejected before birth, she survived and grew a body for herself, driven by an implacable hatred for mutantkind's champion.

Few villains have made an entrance as seismic as Cassandra Nova's — bursting onto the scene in Grant Morrison and Frank Quitely's landmark New X-Men #114 in 2001, she arrived as one of the Modern Age's most genuinely unsettling presences, and Marvel's mutant corner of the universe has never quite recovered. With four key-issue appearances to her name and a publishing history stretching across a remarkable 25 years through New X-Men, Marauders, and X-Men, she's proven herself far more than a one-arc wonder. She keeps rarefied company — Wolverine, Cyclops, Emma Frost, and Logan all share her pages — which tells you everything about the weight Marvel places on her. If you're building a serious Modern Age X-Men collection, Cassandra Nova is essential reading.