Madelyne Pryor, the Jean Grey lookalike introduced in Uncanny X-Men #168, was put through the ringer by writers over the years, as she went from being Scott Summers' wife and Cable's mother to a clone of Jean Grey and eventually a supervillain. You've gotta love any Wikipedia entry that comes with the caveat, "Madelyne's biography has been rendered particularly complicated because of the many retcons involved in the publication history of both her character and that of Jean Grey."
But that wasn't always the plan for the character, as legendary X-Men writer Chris Claremont notes in the video below. The footage is from an interview conducted for the upcoming documentary Comics in Focus: Chris Claremont’s X-Men. Filmmakers were able to reunite Claremont, writer Louise Simonson and editor Ann Nocenti for a discussion of their time working on the X-franchise.