Jean Grey has been pivotal to X-Men storylines in Marvel Comics since their debut in 1963, which made her a clear fit for 2000's X-Men.
Regularly cited as one of the most important female characters in Marvel Comics, Rogue debuted in X-Men portrayed by Anna Paquin and made further appearances in X2, X-Men:
As Rogue's love interest and later husband, Gambit should have been more pivotal to Fox's X-Men franchise. Taylor Kitsch portrayed Gambit in the reviled X-Men Origins.
Despite being a member of the X-Men, X-Force, and the Avengers in Marvel Comics, Sunspot was relegated to a minor role in Fox's X-Men franchise.
In Fox's X-Men franchise, Rogue filled Jubilee's role from Marvel Comics, joining the X-Men as a teenager and adopting Wolverine as her father figure.
Darwin is a relatively new addition to Marvel Comics, only debuting in 2006, but has already made his impact, something which he failed to do when introduced into 2011's X-Men.
Two attempts were made to bring Angel into Fox's X-Men franchise, first in X-Men: The Last Stand, portrayed by Ben Foster, and then in X-Men: Apocalypse, played by Ben Hardy.
Fox never really understood what to do with Psylocke, even going so far as to give her two different power sets in each timeline.
Bishop's origin in Marvel Comics was ignored to enable him to fit better in the storyline of X-Men: Days of Future Past. Originally, Bishop was from a dystopian future,
Elliot Page portrayed Kitty Pryde, a mutant with the ability to phase through solid objects, in X-Men: The Last Stand and Days of Future Past.
The New Mutants, depicted as a patient at Milbury Hospital in a vast departure from her Marvel Comics roots.
While James Marsden was the perfect casting for Scott Summers, a.k.a. Cyclops, Fox completely wasted him.