Coupled with the other previously mentioned deviations, these are some of the main ones I could think of without becoming overly nitpicky, as all adaptations make changes. Also, some of these things have changed in the books, but this is how they were originally introduced during the times of the various films’ releases.
X-Men
- Iceman is one of the five original X-Men.
- Although a run-away, Rogue is originally a villain under the guidance of her foster mother, Mystique. She later joins the X-Men.
- Sabretooth is a brute working for Mr. Sinister’s Marauders instead of Magneto’s Brotherhood.
- Mystique operates her own Brotherhood of Evil Mutants after Magneto’s Brotherhood disbands.
- Jean Grey is not a doctor.
- Iceman does not befriend Rogue.
- Toad does not have a prehensile tongue. He does now, but he didn’t then.
- Henry Gyrich is not killed and replaced by Mystique.
- Senator Kelly is not transformed into a mutant, nor does he die, due to Magneto’s mutation machine.
- Magneto’s mutation machine plot/Liberty Statue confrontation is specific to the movie.
- Rogue’s white streak is not the result of Magneto’s mutation machine.
- The X-Men wear brightly colored costumes. They don’t wear stylized leather uniforms.
X2: X-Men United
- Discovered by Xavier, Nightcrawler is introduced along with Banshee, Colossus, Storm, Thunderbird, and Wolverine. He is not introduced to the X-Men as a pawn of Stryker.
- Arty is a bizarre looking Morlock. He is not a normal looking student at Xavier’s School for Gifted Youngster’s.
- Rogue is romantically linked to Gambit. She is not romantically linked to Iceman.
- Pyro is an adult member of Mystique’s Brotherhood. He is not a student of Xavier’s, nor is he Iceman’s rival.
- Iceman's parents know he is mutant before he is sent to Xavier's School for Gifted Youngsters and he does not have a brother, Ronny.
- Jubilee and Siryn are typically portrayed as older, and Jubilee is more of a sidekick to Wolverine (similar to Rogue in the first X-Men movie).
- William Stryker is a religious zealot. He is not a military scientist, nor is he involved with Deathstryke or Wolverine’s past.
- Lady Deathstryke is a cyborg of sorts who receives her enhancements via Spiral’s Body Shoppe in order to exact revenge upon Wolverine. She is not Stryker’s assistant/bodyguard, and she is not killed by Wolverine.
- The Weapon X labs at Alkali Lake are specific to the movie.
- William Stryker kills his son. Unlike Jason Stryker in X2, he is not loosely based on Mastermind from the comic books.
- William Stryker does not die chained to a cement slab.
- While in space, Jean Grey sacrifices herself protecting the X-Men from a wave of deadly radiation. She immediately re-emerges from Jamaica Bay as Phoenix. She does not sacrifice herself from a wave of water and does not seemingly die at Alkali Lake.
X-Men: The Last Stand
- Nightcrawler does not leave the X-Men upon meeting them.
- Jean Grey is a benevolent young woman and one of the last to join the five original X-Men. She is not an all-powerful brat.
- Angel is one of the five original X-Men. He and his father have nothing to do with the Cure for mutants.
- Leech is a bizarre looking member of the Morlocks. He is not the source of the Cure, nor is he featured in the cure storyline.
- Depending on the books, Phoenix is a result of Jean Grey’s ultimate power as a psi or she’s a separate cosmic entity. Either way, Phoenix is not the result of Xavier’s tampering.
- Phoenix is a good entity before transforming into the bad entity, Dark Phoenix. The movie does not differentiate between the two.
- Phoenix manifests her powers via a fiery aura, or Phoenix effect. In the movie she becomes pale, veiny, and demolecularizes objects.
- Phoenix never kills Cyclops—Cyclops is a staple of the Dark Phoenix Saga and serves as Jean Grey’s anchor throughout. He is one of the reasons Jean Grey is able to keep the Dark Phoenix at bay.
- Phoenix never kills Xavier—Phoenix and Xavier battle, but Xavier temporarily restrains Phoenix.
- Phoenix is mentally manipulated by Mastermind and temporarily joins the Hellfire Club. Magneto and the Brotherhood have nothing to do with the Dark Phoenix Saga.
- Callisto is an unattractive mutant who wears a trademark eye patch and lives in the sewers with her band of Morlocks. She, nor the Morlocks, join the Brotherhood. They are not featured in the Dark Phoenix Saga.
- Psylocke is a member of the X-Men. She is not a member of Callisto’s Omega Muties and never works for the Brotherhood. She is not killed by Phoenix.
- Arclight works for Mr. Sinister’s Marauders instead of Callisto’s Omega Muties and Magneto’s Brotherhood. She also does not die at the hands of Phoenix.
- Juggernaut is Xavier’s stepbrother, who receives his power from the magical gem of Cytorrak. He is not a mutant henchman, recruited by Magneto’s Brotherhood.
- Multiple Man is not a member of Magneto’s Brotherhood.
- Kitty Pryde is romantically linked to Colossus. She and Iceman don’t share a flirtatious relationship.
- Bolivar Trask is a scientist who develops the Sentinels. He is not a Presidential aid.
- Mystique is not cured.
- Magneto is not cured.
- Alcatraz Island is specific to the movie.
- The X-Men battle Jean Grey/Dark Phoenix in New York. She then kills billions of people in a distant star system. Later, the X-Men defend her life in a battle against the Shi’ar Imperial Guard before she kills herself on the moon. The X-Men do not abandon Jean Grey. The Government is not involved, and Wolverine is incapable of killing Jean Grey.
- Rogue does not cure herself.