10 Best Times Superheroes Became Villains

8. Jean Grey - The Dark Phoenix Saga

Jean Grey is one of the noblest X-Men in Marvel history, which is why her turn as Dark Phoenix was such a sight to behold when it first happened.

Although fudged in no less than two separate live action adaptations, the Dark Phoenix Saga is one of the most lauded story-arcs to come from Chris Claremont and John Byrne's run on Uncanny X-Men, and given how it has been fudged so regularly, it stands to reason that not everyone is aware of what actually goes down in the story itself. Here's a brief synopsis:

During a mission in space, the cosmic entity known as the Phoenix finds its way to Jean Grey. Aware that Phoenix is now on Earth, the villainous and conspiratorial Hellfire Club mentally manipulate Jean to join their side, and they prove successful. Jean becomes their new Black Queen, but when she realises she's being mentally controlled, the Phoenix lashes out and takes Jean into space... where she then decimates a life-sustaining star to satiate her appetite.

Countless billions inhabiting a nearby planet perish as a result, and this brings Jean to the attention of the Shi'ar. Grey eventually sacrifices herself to spare the X-Men, but even when she returns the threat of the Dark Phoenix lingers, making this particular turn one of Marvel's most successful.