After Professor X used his powers to shut down Magneto's mind, a small piece of the villain's psyche infected Xavier's own. The resulting entity fed off of the professor's negative emotions, and eventually began acting on its own.
Eventually, Onslaught emerged and revealed himself to be the mysterious betrayer that Bishop had travelled back in time to stop. During the final battle, the majority of the non-mutant heroes present sacrificed themselves to stop Onslaught.
Wanda Maxim off went crazy and used her powers to destroy her teammates in Avengers Disassembled (2004) by Brian Bends and David Finch. This led to House of M (2005) by Brian Bends and Olivier Compel, where Wanda uses her powers to create an alternate universe where mutants rule the Earth.
Also, the premise itself is flawed, as there are countless ways to deactivate mutant powers without killing them. Still, it helped shaped the landscape for the X-Men comics for years to come, and deserves to be remembered.
In Giant Size X-Men #1 (1975) by Len Wan and Dave Cock rum, Professor X recruits a new team of mutants to rescue the original X-Men, who had been captured by the sentient island of Krakow. In Deadly Genesis (2006) by Ed Breaker, it's revealed that this wasn't Xavier's first rescue attempt.
However, one of the missing team members, Vulcan, survived the ordeal and eventually returns for revenge. Vulcan, however, proved to be a popular character and played a major role in several later stories, like War of Kings (2009).
When pieces of Asteroid M begin falling to Earth, the Avengers and X-Men both head to the crash site. Stern was replaced by Tom Deface, who ends the series by having Magneto turn himself in and stand trial.
While Deface is a great writer, it seems like he was brought on to write a different ending than originally intended. For years, the X-Men had dealt with a vague prophecy that predicted that 12 mutants would play a key role in either bringing about, or preventing, a future ruled by Apocalypse.
Apocalypse nearly succeeds, but Cyclops sacrifices himself to prevent the villain from taking over Nate Grey's body. The biggest problem is that the story ends on a bit of a cliffhanger, with Cyclops/Apocalypse still merged and on the run.
That storyline wouldn't be concluded until the following year's The Search For Cyclops miniseries, during which Apocalypse's spirit is killed and Summers is freed. Running through the various X-Men titles of 1997, Bastion is able to capture several key X-Men (including Jubilee and Cyclops), while planning on wiping out as many mutants as possible.
He also activated his army of Prime Sentinels, who were regular people outfitted with nanotech that turned them into mutant hunting robots. This crossover happened immediately after Marvel “killed off” most of their other heroes, and was meant to have the X-Men take center stage.
The X-Men franchise was massive at the time, and fans were forced to buy a ton of issues across several titles just to get the whole story. Aside from that, this was a good story to help move the mutants past the traumatic and world shattering events of Onslaught.
Written by Brian Michael Bends, Matt Fraction, Jason Aaron, Ed Breaker and Jonathan Hickman, and drawn by Adam Hubert, John Romina Jr and Oliver Compel, the event took over most of Marvel's lineup. Eventually, the Phoenix possesses Cyclops, Emma Frost, Enamor, Colossus and Magic.
The five begin to force their will upon the world, culminating in a final showdown that left Professor X dead and Cyclops' heroic reputation forever tarnished. NYC is transformed into a hellish landscape, forcing the majority of Marvel's heroes to fight off the demonic horde.
Eventually, the demons are defeated and banished, New York is returned to normal, and Jean Grey takes down Pryor. There's plenty of action, and many of the tie-ins gave great excuses for artists to go nuts drawing the demonic invasion.
If anything, it's worth reading to watch an elevator eat a family in the Empire State Building. After Jean Grey was killed off during Born/Magneto's attack on New York in Grant Morrison's run on New X-Men, the Shi'Ar resurrect the Phoenix force.
The X-Men help give her the strength to finally put the Phoenix to rest, and Jean returns to “the White Hot Room” (aka death). Due to Jean Grey's history of dying and being resurrected, many fans assumed that her death in New X-Men wouldn't be permanent.
While she was eventually revived, End song helped cement her status as deceased for over a decade. It ultimately reveals the existence of thousands of clones of them, who were all partially developed using Emma Frost's DNA.
During Extinction Agenda (1990), it's discovered that Cameron Hodge has turned the island into a mutant slave camp. When Hodge eventually betrays the Kenosha, the government is forced to team up with the X-Men to take the madman down.
This event is famous for being one of the first major storylines to feature both Jim Lee and Rob Ziegfeld. Of course, using different artists for each chapter leads to several glaring continuity issues (like characters randomly switching outfits).
Cameron Hodge would return and continue to be one of the X-Men's strangest (and most frightening) foes, so this event is worth remembering just for his inclusion. The original five students formed their own group, X-Factor, while the main X-Men moved to Australia and pretended to be dead, before briefly disbanding.
When the two teams discover that Muir Island has been taken over by the Shadow King, they both head over to free their allies. The Shadow King eventually jumps into Legion's body, granting him an extraordinary amount of power.
Jean Grey is eventually able to pull the X-Men together to defeat the villain, although the battle leaves Legion temporarily brain-dead. It features several classic X-Men writers and artists, including Chris Claremont, Andy Hubert and Fabian Nicaea.
It starts off during an awkward time in the team's history, however, so it might be slightly confusing for newer readers. In 1987, Marvel pitted the mutants against their first family in Fantastic Four vs the X-Men by Chris Claremont and Jon Bogdanovi.
The series starts with the X-Men needing Reed Richard's help to cure Kitty Pride, who was wounded during the Mutant Massacre (1986) storyline. The Fantastic Four, however, are reeling from the recent discovery of a journal that suggests Reed knew what would happen during their fateful flight.
The X-Men, wary of owing a debt to Doom, reluctantly agree, except for Kitty, who would rather just fade away than put the X-Men in a bad position. The only reason why it isn't ranked higher on this list is because it's more of a Fantastic Four story that guest stars the X-Men.
Bishop chases him, believing that the newborn might cause his own horrific future to come into being. In Messiah War (2009), X-Force follows them, finding a world ruled by Cable's evil clone Strife.
The story ends on an ominous note, as Emma Frost believes that Hope might be a future host for the Phoenix, along with the appearance of five new mutants across the globe. It helped give direction to the overall story and show that there was a future for mutants at Marvel.
Cyclops and Jean Grey are kidnapped by Strife, who reveals they are his “parents,” making Scott the true father of Cable. Still, the story itself is very good and is fairly easy to follow, despite being 12 issues (minus the epilogues) spread across four different series.
Much to X-Factor's shock, Death is revealed to be a transformed Warren Worthington, who was believed to be dead at the time. Angel's transformation into Archangel is one of the most traumatizing events to occur to an X-Man, and still effects the character to this day.
Days of Future Past appeared in Uncanny X-Men #141 and #142 (1981) by Chris Claremont and John Byrne. An adult Kitty Pride has her mind sent back to the past, where she possesses her younger body.
She has to convince the X-Men to believe her and help stop the assassination of Senator Robert Kelly (who is fiercely anti-mutant). The X-Men are successfully able to stop the Brotherhood of Evil Mutants from killing Kelly, and Pride returns to the future.
The story ends without showing if the future has been changed or not, with the X-Men wondering if the dark dystopia is still waiting for them. “Days of Future Past” has been adapted several times for various X-Men television shows, and was even the basis for the plot of a film in 2014.
During the funeral for Island Rasputin, Magneto returned to Earth and announced his intentions to kill all of humanity. He and his Acolytes have set up their base on an asteroid called Avalon, from which they plan to launch their attack.
After Magneto unleashes a devastating electromagnetic pulse across the globe, Xavier leads a team of X-Men to Avalon, where they confront the villains. In one of the most brutal fights to ever occur in an X-Men book, Magneto rips the adamantine from Wolverine's skeleton.
Not only did it affect Wolverine's story for years to come, it laid the groundwork for events that would shake the entire Marvel universe. Xavier's mind-wipe ultimately led to the creation of Onslaught, who caused the “deaths” of both the Avengers and Fantastic Four.
He discovers that they've been kidnapped and replaced by the Phalanx, who are attempting to use cerebra to locate the next generation of mutants. Forced to team up with enemies Emma Frost and Saber tooth, Banshee must find the young mutants before the Phalanx does.
Meanwhile, Cyclops and Jean Grey team up with Wolverine and Cable to rescue the X-Men from the hive's clutches. Banshee is a great character, and this story gives him a chance to take center stage.
Chris Claremont, Dave Cock rum and John Byrne created one of the most epic X-Men stories with The Dark Phoenix Saga. It begins with Jean Grey seemingly dying as the X-Men return from an adventure in space, only to re-emerge as the Phoenix, a being of pure thought.
Her power levels are off the chart, and Dark Phoenix destroys an entire solar system, killing billions. Its impact is still felt to this day, with the Phoenix still having a deep connection with Jean Grey.
Not only that, but the ensuing battle caught the attention of Apocalypse, causing him to put his plans of world domination into motion a decade earlier than he originally did. Without Xavier to lead the X-Men, Apocalypse successfully takes over North America and launches the Earth into a brutal world war.
Characters were radically changed, with Cyclops and Havoc becoming villains, and Magneto taking a heroic turn as the leader of the X-Men. Eventually, a time displaced Bishop is able to travel back to the past again and prevent Legion from killing Xavier and waking Apocalypse, correcting the time stream.
This was just in time, as a salvo of nukes was headed towards New York City in hopes of destroying Apocalypse's forces once and for all. Several characters escaped to the mainstream Marvel Universe, such as Nate Grey and the villains Dark Beast and Sugar Man.