Professor Charles Xavier was the leader of the X-Men, a group of mutants who were trying to seek peace with the human race, educate young mutants in the responsible use of their powers, and stop Magneto from starting a war with humanity. The team is based at a Xavier's School for Gifted Youngsters, run from Xavier's Westchester mansion. The base included subterranean medical labs, a training facility called "The Danger Room," an aircraft hanger, and Cerebro.
X-Men: First Class
Prior to the formation of the X-Men, Professor Charles Xavier and his associate, Raven Darkholme, were contacted by agents of the CIA to help investigate the Hellfire Club, a clandestine organization of mutants with suspected criminal operations. The association with the CIA soon brought Xavier into contact with other mutants, including Erik Lensherr, Havok, Darwin, Beast and Banshee.
Xavier's mutant group then came into conflict with the Hellfire Club, which led to the murder of Darwin at the hand of the Hellfire Club's leader. Xavier resolved to stop the Hellfire Club and began training his young group in preparation for conflicts to come. During subsequent confrontations with the Hellfire Club, Erik and Charles' views regarding the path of the emerging mutant race diverged, resulting in the end of their friendship and the fracturing of their emerging team. Erik, now going by the name "Magneto", left to form the Brotherhood of Mutants, with Darkholme following him, while Xavier continued to shape the others into a team with a higher purpose: the X-Men. 
Not long after Xavier's School for Gifted Youngsters opens, the war in Vietnam starts and intensifies, causing many of the school's students and faculty to leave. Xavier eventually shut down the school, and he and Hank isolated themselves within the mansion. 
X-Men Origins: Wolverine
William Stryker sent his son Jason to Xavier's school in hopes of ridding his mutation, regarding it as a disease that he believed needed be cured. Xavier had no interest or belief in 'curing' mutants, which angered Stryker. Later, Xavier helped liberate the mutant children held prisoner by Stryker at Three Mile Island. He took them in an flew off in his helicopter with Scott Summers and Emma Silverfox.  Summers would go on to lead the X-Men. 
After finding Jean Grey, Xavier began controlling her with telepathic blocks because he believed her class 5 powers were too much for her to handle. Her bottled up powers manifested themselves as an id-like alternate personality called the "Phoenix" — a purely instinctual creature, ruled only by its own violent desires.
At some point he recruited Ororo Munroe who also became X-Man.
In Canada, Cyclops and Storm saved Wolverine and the young runaway Rogue from the Brotherhood's Sabretooth and brought them to the X-Mansion. Xavier offered to help Wolverine learn the secrets of his forgotten past.
Mystique infiltrated the school and sabotaged Cerebro. When Xavier used Cerebro he fell into a coma. Despite his absence Wolverine and the X-Men prevented Magneto from mutating the leaders at the World Summit on Liberty Island. Magneto intended to use Rogue's ability to absorb other mutant's abilities on himself so that Rogue could power his machine. Placing his hand to her face, Wolverine succeeded in transferring his regenerative abilities to a dying Rogue, saving her. Professor Xavier recovered from his coma and Magneto was taken into custody.
Later, Xavier visited Magneto in his plastic prison cell, and the two played chess. Magneto warned his friend that he would continue his fight, to which Xavier promised that he and the X-Men would always be there to stop him. 
X2: X-Men United
William Stryker began experimenting on mutants, using a drug injected directly into the back of the neck to control them. He used Nightcrawler, a teleporting mutant, to orchestrated an attack on the President in the White House, but Nightcrawler failed and escaped. Storm and Jean tracked Nightcrawler down.
Cyclops and Professor X were captured by Stryker and his assistant Yuriko Oyama. Stryker had his troops raid the X-Mansion with the soldiers sedating every student they could find. Some were taken to Stryker's base located at Alkali Lake, inside the dam, while others escaped. Wolverine, along with Rogue, Iceman and Pyro, escaped to Iceman's home in Boston. After a 9-1-1 call by Bobby's brother Ronnie, the police arrived leading a dispute with Pyro. Jean and Storm arrived in the X-Jet to pick them all up. The X-Men teamed with Magneto and Mystique to stop Stryker.
Stryker had stolen enough equipment from Xavier's own Cerebro unit to build a second Cerebro, with which he planned use to kill all of the world's mutants. Stryker gained control over Professor Xavier through his son, Jason Stryker, who was able to project powerful visions in the mind, blinding a person to reality. Professor X was instructed to use Cerebro to find and kill all existing mutants. Mystique, disguised as Stryker, used Jason to convince Professor X to kill all humans. Nightcrawler teleported Storm inside of Cerebro, where she freed the Professor from his telepathic illusion.
Jean, Magneto, and Mystique were attacked by a brainwashed Cyclops on their way to rescue Professor X, causing damage to the generators that kept the dam from collapsing. The force of Jean's telekinetic blast awakened Cyclops from his brainwashing. Wolverine found Stryker in an adamantium smelting room along with Lady Deathstrike. Wolverine and Deathstrike fought. Wolverine was forced to kill her. Magneto and Mystique used Stryker's helicopter to escape Alkali Lake, chaining Stryker to concrete rubble. Wolverine found Stryker on a landing pad, where Stryker attempted to bargain for his life Wolverine. Wolverine left him for dead.
A malfunction aboard the X-Jet prevented it from taking off, and the dam finally burst. The flood got stronger, drowning Stryker. Jean left the jet and created a telekinetic wall in order to stop the wave, and at the same time raised the jet above the flood waters, all the while surrounded by a corona of fire. Jean activated the X-Jet's primary engines before releasing the torrent of water down on herself.
The X-Men were able to supply the President with files from Stryker's private offices. Professor X warned him that humans and mutants would have to work together to build peace, or they would destroy each other through war. Rogue and Iceman were promoted to X-Men. 
X-Men: The Last Stand
A pharmaceutical company called Worthington Labs announced that it had developed an inoculation to permanently suppress the X-gene that gives mutants their powers, offering the so-called "cure" to any mutant who wanted it. The cure was derived from a mutant boy named Jimmy. While some mutants were interested in the cure, including Rogue, many others were horrified by the announcement.
In response to the news, Magneto decided to raise an army, warning his followers that the cure would be used to exterminate the mutant race. Magneto ambushed a military transport and freed Juggernaut, Mystique and Multiple Man, during which Mystique blocked a shot of the mutant cure aimed at Magneto, only to be left behind because she was not "one of them" anymore.
Cyclops, still heartbroken about the loss of Jean Grey, returned to Alkali Lake. Jean appeared to Cyclops, and as the two kissed, Jean changed killed Cyclops. Sensing trouble, Professor Charles Xavier sent Wolverine and Storm to investigate. When they arrived, the two X-Men encountered an unconscious Jean. The majority of Jean's power was seated in her unconscious mind and her powers were largely fueled by instinct, and not under her complete control.
Jean pleaded with Wolverine to kill her before she could harm anybody else, but when he refused the Phoenix surfaced and fled to her childhood home. Magneto, also aware that Jean's powers were loose, met Xavier at Jean's house. The two men pleaded for Jean's loyalty until the Phoenix resurfaced, unleashing her devastating power. Furious at being caged within Jean's subconscious for twenty years, she destroyed her family's house and engaged in a psychic battle with Xavier. She eventually overpowered and disintegrated Xavier, then left with Magneto, temporarily weakened.
The X-Men regrouped and confronted Magneto's army, which was attacking the pharmaceutical company's laboratory on Alcatraz Island, which was being guarded only by a company of soldiers. During the battle, Kitty Pryde saved Jimmy, Iceman went one-on-one with Pyro, and Beast injected Magneto with the cure, nullifying his mutant powers. Wolverine nearly coaxed Jean back to sanity. However, after the soldiers fired upon Jean the Phoenix quickly emerged and began to disintegrate everything and everyone around her. Wolverine fought his way to Jean, relying upon his healing abilities to save him from her destructive power. Momentarily gaining control, Jean begged Wolverine to save her. Telling Jean he loved her, Wolverine reluctantly killed her with his claws.
Despite the X-Men's losses, life went on. The school continued, even without Xavier. Pained by her inability to get physically close to her boyfriend, Rogue decided to take the mutant cure. Magneto, now an ordinary man, sat at a chessboard and reached out toward a metal chess piece that trembles slightly — indicating that the cure might not be as permanent as originally thought.
Not long after the events on Alcatraz Island, the X-Men disbanded due to their few numbers (though the school remained active). However, Magneto and the restored Professor X soon realized that the team needed to re-assemble for a problem with ramifications on all mutants. Together they gathered many of their pupils, though only Wolverine was shown being recruited. 
Days of Future Past
Former X-Men Kitty Pryde, Iceman, and Colossus teamed up with Sunspot, Bishop, Blink, and Warpath to help survive against the Sentinels. The plan was that since Warpath can detect Sentinels, he would alert them so they could get ready and fight the Sentinels while Kitty sends Bishop's mind back a few days to alert them of the coming attack. Blink scouts the next location and they're gone before the Sentinels know they're there.
They meet up with Xavier and the remaining X-Men at a Chinese monastery. Pop while Kitty sends Wolverine's mind back in time, the others prepare for battle. After a unknown amount of time, Warpath detects 12 Sentinel ships headed their way. Storm creates a Storm that takes down a few ships but the majority of them remained and began to release hundreds of Sentinels. She then sends a lightning bolt at Bishop to power him. Blink opens a portal towards the Sentinels and Bishop fires into it. Magneto lifts the X-jet into the air and sends it flying towards the Sentinels. Storm sends a lightning bolt at it's fuel cell, which blows up destroying the thousands of Sentinels. The debris hits the monastery, but Magneto is able to stop most of it, but is stabbed by a piece of shrapnel.
The X-Men turn to look at Magneto, when a Sentinel jumps up and stabs Storm in the back and throws her off the cliff. Bishop then fires at the Sentinel. The team looks up to see dozens of Sentinels climbing down the mountain towards them. Three Sentinels surround Bishop and fire onto him. He absorbs the blast to the point where he explodes. Sunspot lights himself on fire and flies up, setting Sentinels on fire. Magneto uses the X-Jet debris to seal the vault even further. Blink then teleports him inside where he makes peace with Xavier and dies. Blink opens a portal and Colossus jumps through it, sending him into the sky. After building up enough momentum, Blink sends him flying into a sentinel.
The X-Men make their last stand as they buy as much time as possible. Colossus throws a punch at a Sentinel, which jumps over him and grabs his arms as another grabs his legs and they pull until he is ripped in half. Warpath jumps onto a firing Sentinel, only to be pulled in to it's blast. A Sentinel turns into a diamond form and another into a Rock form to combat Sunspot's fires and surrounds him. One cuts off his arm and then kicks him to another Sentinel, which stabs him. Sentinels fire onto Blink, but she redirects the blast at other Sentinels but is eventually overrun and stabbed to death.
The Sentinels make their way into the vault. Iceman tries to freeze it but with little success. The Sentinels fire onto him, painfully killing him. They turn to execute Kitty and Xavier, but then the timeline is changed forever as Mystique drops the gun and spares Trask. 
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