X-Men: Jean Grey
This marks the third entry into the X-Men run through on the character named Jean Grey. Jean was a part of the first group of X-Men and the only female member of the group for a extended period of time. Jean may have been one of the more powerful members of the X-Men as her telepathy and telekinesis powers at times were stronger than that of Professor Charles Xavier. She also become something more with the Phoenix Force. The Phoenix escalated her powers to an unimaginable level, so much so that she could fly while surviving in any atmosphere and be able to fly in outer space. She even has the ability to create star gates to travel anywhere in the universe instantaneously. Her most deadly ability is her cosmic flames she is able to emit under any circumstance.
Jean Grey had a relatively normal life until her mutant powers manifested when she turned ten years old. She didn't know what they were or how to control them, and neither did her parents. Her parents turned to Charles Xavier who was running a school for gifted children. Xavier promised to treat Jean, and in fact used her to fine tune his Cerebro machine that he used to find other mutants alike. Xavier than introduced Jean to the astral plane, a place that only telepaths like themselves could reach. While there, part of Jean's mind appeared as a Phoenix raptor and managed to touch the mind of Scott Summers as he slept peacefully in an orphanage. Upon seeing Jean's great power, Xavier placed psychic shields in her mind to prevent her from being able to use her abilities until she was mature enough to use them. Eventually, when Jean matured enough, she became a founding member of the X-Men alongside Hank McCoy (Beast), Scott Summers (Cyclops), Bobby Drake (Iceman) and Warren Worthington (Angel). Jean used the name Marvel Girl for quite some time, which was quickly dropped as people more frequently called her Jean.
The X-Men were eventually tasked with a mission that involved going into outer space on a shuttle, and the Phoenix Force took notice of Jean's great potential. Jean then had a vision about becoming the Phoenix, and the immense amount of power that came with it. The memories of the vision quickly disappeared almost immediately after she had the vision. Over time the X-Men began to grow as more and more mutants came to mansion such as Wolverine, Storm, Rogue, Gambit, Jubilee and so on. Jean and Scott began to fall for each other after spending so much time together. Despite her strong feelings for Scott, she did have a soft spot for Wolverine as well but never loved him the way she did Scott. The X-Men went to space in the first place to defeat scientist Stephen Lang who had created a space station where he was creating Sentinels. A massive robotic army set with one goal, to destroy all mutants. After destroying the station, the X-Men escaped by jumping into a shuttle headed for Earth, however it was traveling through a lethal solar radiation storm. Jean was the only one that was unprotected from it, as she made sure everyone else was safe before she jumped into a sealed off corridor with them leaving her locked out and dying in front of her friends of radiation poisoning. Jean was saved by the cosmic entity known as Phoenix Force. It created a duplicate body for her complete with her memories, personality while also absorbing a portion of her consciousness and cast her to the bottom of Jamaica Bay in suspended animation in a cocoon of sorts.
For months the Phoenix roamed the Earth believing herself to be the real Jean Grey. At one point she even saved the universe by healing the M'Kraan Crystal. The crystal was a source of a near limitless power that could pull and trap all matter inside of it. However, everything went to hell when the villain named Mastermind used his mental manipulation powers on Phoenix causing her to go insane and become the Dark Phoenix. This indirectly caused a portion of Jean's consciousness within the Phoenix to resurface and commit suicide. That side of Jean then journeyed to the great beyond and in the afterlife she met an incarnation of Death that explained the Phoenix Force to her. She then dawned a new uniform as she was then sent back to her original body complete with her consciousness and some residual Phoenix energy only to be rejected. After being rejected, she was sent inside her clone, Madelyne Pryor and eventually Jean was rescued from her stasis. Jean and the other original X-Men formed a new team called the X-Factor. Pryor and Jean faced off against each other, in a Highlander sort of way (There can only be one!), and Jean won the fight. As her prize she absorbed both Madelyne's personality and the Phoenix' personality as well as some Phoenix energy causing her to become one of the strongest mutants. She eventually lost the personalities while keeping some of the memories when she expelled the Phoenix energy in a fight against a Celestial on an alien world.
Jean and Scott tied the knot when she eventually rejoined the X-Men. The couple didn't have a lengthy honeymoon as the two were temporarily teleported to the future with Cable, their son from the future Nathan Summers. Upon arriving in the future the two were tasked with saving the future from the likes of Apocalypse. Apocalypse was trying to gain the power of the Twelve, and in order to do so he believed it to be tied to Cable but in fact he needed Scott to be the host. Apocalypse needed to take Twelve mutants for him to absorb to give him god-like powers to re-create the world in Apocalypse's image. Many of the Twelve were indeed members of the X-Men, and to make matters even more worse, they had assembled to topple his plans but only fell before him. Apocalypse preferred Nathan, but Scott offered himself up to spare his son from being the twelfth. Right before Apocalypse was done absorbing Scott, Jean removed his essence which in turn foiled Apocalypse's plan. However, when Scott was placed back into his body, he still had remnants of Apocalypse's corruption coursing through his being. This is in turn, put a strain on their relationship but like Rogue and Gambit, the two couldn't stay apart for long.