Annie Richardson Uncanny X-Men 241

Annie Richardson was Jean Grey's best friend until the day she was hit by a car and died. The shock of seeing her friend's death was so traumatic that it activated her telepathic powers. It also led to her creating an alternate personality that called itself, the Phoenix.

Annie (or an aspect of her) remained in Jean's consciousness, and helped Jean and Phoenix reconcile, allowing Jean to draw on Phoenix's powers when needed.