Was Big Boss' story defined and known prior to MGS3? Like, I don't know, written in some sort MGS bible or something? Or he was still treated as a unknown figure from the early Metal Gear games that was somehow related to Solid/Liquid Snake?
There was enough written in supplemental material (official guides, manuals, etc.) that there was a subset of people that thought it *wasn't* going to be Big Boss and it was another MGS2 bait and switch right up until Metal Gear Solid 3 came out.
Originally, Big Boss was way older, old enough to fight in World War II (this is why Liquid claims he was in his late 50's when he and Solid were created). He also lost his eye in the 1980's due to shrapnel from a landmine going off and it was what made him retire from the mercenary world and form/command Foxhound. (MGS V added an additional coma to the background as well.)
There might have been other stuff about him (I seem to recall small things like Big Boss was Times "Man of the Year" and stuff like that), but those were the *big* changes to his established background that I remember before MGS3. I'm pretty sure the rest of it was pretty much what they stuck with, worlds most famous mercenary who fought in various conflicts throughout the 70's and 80's.
I definitely like the idea of MGSV not being real.
For all of V's faults though, riding a horse through Afghanistan while listening to "Behind The Drapery" was one of the most "this is fucking COOL!" moments I've had in gaming over the last ten years.
I mean I don't think there's any faulting MGSV's gameplay, it was just the story that was a mess.
It's honestly the interpretation I go with in my head. I like MGS V's gameplay even if it feels half baked, but the story is just too fucking ridiculous even for Kojima. Back when I cared more I actually took the time to figure out all the details that didn't make sense, but these days the only things I care to remember are that it made no sense that the signal for Ocelot was "V has come to" when "V" was the one who was kept under sedation and Ocelot and Big Boss supposedly brought him out of it themselves, and the fact that there's like a 30 minute time gap Kojima deliberately shows off between Ocelot rescuing Big Boss from the Ambulance crash and returning for Venom which makes no fucking sense when Cypher AND the man on fire were literally just a quarter mile away from them in helicopters chasing them.
It's like you either have to acknowledge that Kojima clearly had something else going on in the background, or he's just didn't give a fuck/just wrote the entire "truth" scenario horribly. Now, I'm one to readily say that Kojima is a fucking hack, but the guy put a whole subplot in the game where Venom Snake completely hallucinates events involving him, Ocelot, Miller and Paz being together, talking, recording audio tapes etc. etc. so even I'm going to say he clearly wanted the idea that Snake was suffering from some form of delusions/hallucinations/psychosis to be present.