If you don't know who the X-men are, please open a new tab and open its Wikipedia entry. Or you could read my brief and shitty explanation here.
1963: Stan Lee gets even more drunk while creating the Marvel Universe. Decides to write a story about "The Mutants", in which five white children and their equally white (and somewhat pedophillic) teacher with superpowers are a metaphor for all minority groups. Editor thinks the title is bullshit. Renamed the X-men. With an "X" for X-traordinary. Magneto is introduced. The fanbase hasn't established themselves enough to go crazy.
1975: Fucking kids got themselves lost on an island. After getting another group of kids killed while trying to rescue the first group, Xavier gives in and recruits a bunch of adults. The X-men get multicultural. Fanbase establishes and proceed to worship Claremont like a god.
1975- Almost present: Stuff happens. Four movies, three cartoons, and one anime are made. Jean dies but doesn't then does. The Summers win the award for "most confusing family".
Now: Mutants are off the endangered species list. Logan's headmaster. Scott fixed things but got crazy and killed Xavier (the father figure who was in love with his wife but never ditched him to become a space pirate like his real dad). Relaunch time!