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But it still keeps the one question of who is Mr. X.
Mr.X is a tyrant in a steel suit. I'm convinced that as Capcom developed the various RE games, they never did have a "complete" story. They just tried to make the story of a new game blend in with the old ones and hope things matched up. Actually you can find a HUGE Resident Evil story evalution at gamefaqs, it explains everything.
As for the order to play the games, I'd say play them in the order of release, so you never know less than the creators. This means get out your old PSX and play the original RE, RE2, and RE:Nemesis. If you do, you'll appreciate the remake of RE a lot more.