Metal Gear's story is a mess. Hideo Kojima might make great stealth games, but, the dude also needs an editor.
With Metal Gear Solid V (and its prequel) on the way, there might be people who have never played a Metal Gear game before wanting to get in on the action. Or veteran players who might be out of the loop and want to get back into things.
If that's you, then may God have mercy on your soul, because AudioRejectz's guide -- while being as concise as it could probably be -- is still some heavy reading.
Thankfully, it's also in bullet-point, chronological form, so you can also use it as a mid-game reference for all those "huh?" moments.
Know that there are some spoilers, but the big ones have been kept secret where possible.
Metal Gear - The complete story [Reddit]