3. Jean Grey
There was actually a time in comic book history when the X-Men werent the big dogs on the superhero block. Not only were they behind the Avengers and the Fantastic Four but for a good while in the 70s even the Defenders and the Guardians of the Galaxy outsold them. All that changed when a new team of mutants was introduced in Giant Sized X-Men #1 in 1975 by Len Wein and Dave Cockrum but it was the death of a character from the first class of X-Men that made the comic the best seller it is today. Jean Grey nee Marvel Girl nee Phoenix nee Dark Phoenix was introduced along with Professor Xs other mutated students, Cyclops, Angel, Beast, and Iceman in X-Men#1 in 1963 to battle with their arch nemesis, Magneto. Jean or Marvel Girl, as she was known then, was the telekinetic of the group as well as the requisite weak female member like the Invisible Girl in the Fantastic Four and the Wasp in the Avengers. She acquired the additional power of telepathy shortly after her and the team were introduced but still had as much impact on the 616 as her mates back then, which is to say very little. It wasnt until the new team was made up of new members like Storm, Nightcrawler, Colossus, and break out star, Wolverine that the X-Men and Jean Greys Q rating began to rise. In the hands of Chris Claremont as writer with assists from John Byrne, Dave Cockrum, and Terry Austin, Jean became Phoenix, a cosmic being on the level of Thor, the Silver Surfer, and eventually Galactus. She also lost her ever lovin mind and morphed into Dark Phoenix, a destroyer of solar systems and alien races. The galactic and the editorial powers of the Marvel Universe could not let that stand and set out to make her pay for the crimes committed under her cosmic temporary insanity. Despite her mates sticking up for her and battling the Shiar Empire on Earths moon, Jean destroyed herself rather than let Dark Phoenix corrupt her further in the culmination of The Dark Phoenix Saga in the classic X-Men #137 in 1980. Cremation is usually the end of the story for not just all of us who read four-color adventures but for the characters as well but Jean Grey was special and it wasnt long before Marvel Comics played around the edges of re-introducing her back into proper continuity. That was done six years later in a two-part story stretching across the Avengers and Fantastic Four titles leading to the original X-Men coming back together in a book titled X-Force. It was retconned that Jean Grey wasnt the one who died on the moon but a being known as the Phoenix Force that had taken over Jeans identity while letting the original cool her heels in the bottom of a bay in New York. It wasnt long until Jean had re-integrated herself back into the X-Mens never-ending battle for the mutant way and even took time out to marry her true love, Cyclops. All well and good until she started tapping into the Phoenix Force again but instead of sacrificing herself again she was killed this time by a Magneto clone in NEW X-MEN#150 in 2003 to become the only superhero on this list to die twice. A neat trick that.
IMPACT: Wolverine is the undisputed star of the X-Men sub-universe of Marvel Comics but he and his team have reached the heights they have because of Jean Greys (supposed) sacrifice on the Moon over thirty years ago. Other members of the X-Men like Mimic and Thunderbird had passed on before that but Jeans suicide struck a chord with comic readers that enabled the X-Men to take their place as the alpha team of not just the 616 but all comicdom. Since 1980, X-MEN has been at or near the top of comic book bestseller lists and crossed over into video games, cartoons, and five top grossing movies because the public caught up to the concept and the original weakest link laid down her life to accomplish thattwice.
OPINION: I came to the X-Men two or three years after The Dark Phoenix Saga but it still cast an ominous shadow over the team that I wanted to learn about in the days before comic books shops and omnibus collections. When I finally got my hands on the trade of the arc, I understood why Jean Greys shadow stretched so long because I almost fell to my knees just like Cyclops when Jean fired that laser cannon at herself. Good stuff and why in my own personal continuity I say it was Jean Grey and not some cosmic entity that died on the Blue Area of the Moon because only a human would pay that cost.