10. Moira MacTaggert
Moira MacTaggert is an incredibly likable character. Her combination of cheerfulness and intelligence is contagious, and maybe that's part of what created her greatest flaw. Her son Kevin, a.k.a. Proteus. In her younger days, Moira was forced into a marriage with a cruel man who she didn't love, and after her husband raped her, she had Kevin, who eventually developed a mutation which broke down his body, forcing him to need others' bodies to survive. Moira developed a chamber in which Kevin could survive until a solution could be found, but after spending years in the chamber, Kevin went insane. Talk about having a skeleton in your closet, and then having to face it€”ultimately in the form of your ex-husband who physically attacked you, no less. Proteus provided an astonishing conflict for Moira. Regardless of Moira's motivations, her actions in regards to Kevin blur the lines of what was under her control. Finding out about Proteus was a bombshell if I ever read one, and this was in an older X-Men story no less, where bombshells happened almost as much as Professor X getting angry for no reason.