JEAN GREY

When Professor X died battling the subterranean Grotesk in X-Men #42 (1968), the X-Men buried their mentor and tried to carry on without him. Only one of them was acting. The man in the grave was not Charles Xavier at all, but the reformed villain Changeling, who had learned he was dying and begged to make amends by taking Xavier's place — while the real Professor hid in seclusion, preparing a defense against the approaching Z'Nox invasion.

Xavier needed one accomplice inside the school to help his double maintain the impersonation, and he chose Jean Grey. She alone knew the Professor she took orders from was an impostor wearing his face, lent a portion of Xavier's own telepathic power to sell the deception. When Changeling died in Xavier's shape, Jean had to grieve in public for a death she knew was staged — comforting teammates whose sorrow was real while hers had to be performed.

The secret held until X-Men #65 (1970), when the living Xavier finally walked back into his students' lives and Jean burst into tears of relief that the pretence was over. For roughly two years of publication, the youngest-feeling burden on the team belonged to its telepath-in-training: keeping a straight, sorrowful face over the biggest secret in the X-Men's history.