A strange thing happened on the way to 1986 ...
Gary saved D&D, and in true Lannister fashion Lorraine Williams had D&D's Ned Stark beheaded.
Most of us in the rank and file of the TSR customer base, knew nothing about it. I didn't for years afterwards. All I knew was that D&D began to change with UA (the AD&D 1.5 era) and changed even more in the 90's with the advent of 2e.
At the time I was a junior in High School, and for all I could tell, all was well in D&D land. I bought Unearthed Arcana, and was only a little dismayed by the new classes, the power creep and the idea of cantrips--but we rolled with it. I also bought Manual of the Planes, Dungeoneer's Survival Guide, Wilderness Survival Guide and eventually picked up a copy of Oriental Adventures; though I was admittedly least excited about it. I'll also admit to hardly ever using these resources at the table, and only reading them in patchy form at best.
For all practical purposes, D&D for us was confined to the AD&D PHB, DMG, MM, MM2, the Fiend Folio, and only occasionally the Unearthed Arcana. And, yes, we played it a little more OD&D with supplements, than true AD&D btb. Lots of others have found they did the same. However, what we did do was resort to the rules whenever questions arose about what was or wasn't allowed. DM Fiat was always capable of being overturned if an official ruling could be found. That was even true if it was found in Dragon Magazine most of the time. We considered Dragon mostly as suggestions, unless it was in a Sage Advice or some other specific rule clarification. But those situations came up infrequently at best.
How was it then, that we developed such a reverence for all things TSR, and specifically Gary Gyax? For us, bitd, the two were synonymous anyway. At least until 2e came along and we eventually heard that Gary was no longer at the D&D helm. And when that revelation was made known, it all made sense to us. UA and the later products were a little un-Gary like (and hence un-AD&D like) to us in retrospect. (Even though Gary's name was on a couple of these works, we assumed he didn't write them. It would be much later that we understood these were works Gary rushed to print to earn some hardback cash for TSR to save the company. And it worked by the way. But they still kicked him out.) And 2e was clearly not AD&D. Which didn't stop us from adopting a few things that seemed like good ideas from the new edition, namely cleric domains, school of magic and d10 for initiative. We hadn't altogether rejected TSR after all.
I stopped gaming in about 1995 or so. 14 years of pretty much AD&D is where I left off. I picked up at the tail end of 3.5 in about 2006 or so. Surprisingly, it took me not too long to figure out 3.5. Just about the time I started playing again, however, they were talking about a new edition! It took a lot longer to figure out 4th edition, and about as long to realize I hated it. And to realize I hated all of it. I started my blog in 2008 and spent most of the rest of the time trying to get back to where I felt like I belonged. I haven't gotten there yet.
The funny thing is that the place I feel like I belong simply doesn't exist anymore. D&D has created certain sorts of players over the course of its evolution. In truth, they are all D&D players, since anyone playing roughly the same game are all playing with the IP that is D&D. Nonetheless, each "age" saw it's kind of player develop:
Pre 1977 Players: Some players really only familiar with the Original D&D books. Some allowing, some not what supplements were played with. Many just "imagining the hell out of" their games. A large portion of these are also lumped into the Pre 1978 crowd.
1977 Holmes Players: Some, who heard that D&D was on its way out and that a rewritten game was coming, chose to transition to Holmes. I've heard some waited to see AD&D, but returned to Holmes because it was closer to their OD&D game. Most Holmes players were new comers to D&D who come through this edition.
Pre 1978 AD&D Players: Before and after the advent of the PHB, there were players who were basically playing with what would become AD&D rules, but did not really ever adopt the advanced rules. Even if they bought them they did not use them btb and felt no real compunction to do so. Many just kept playing their OD&D.
1979 AD&D Players: these are those who adopted the Advanced rules, bought these books and firmly maintained they were playing Advanced D&D. They may not have played with every rule, or even known them, but they deferred to these rules and considered them authoritative. That is after all, what TSR told us to do. This was the game, the "adult" game, as many saw it. Some returning to old school gaming have went back to this time, and left AD&D during the OSR when they saw it in retrospect as flawed or "not really the way they played." Some of these players would grow up to become Pre 1985 Gamers, and some go even beyond that to '89 or 2e and on.
1981 BX Players: These players came into D&D or chose to migrate to the new B/X, mostly from OD&D or Holmes. Many would go on to Mentzer and eventually RC, some to AD&D, some back to Holmes, and some would stay here.
1983 Mentzer players: the Red Box brought in lots of players to D&D and many die hard "basic" players would see D&D as synonymous with red box. And many of these players went on to become RC players.
Pre 1985 AD&D Players: Unearthed Arcana was a watershed moment for more than just Gary Gygax. Many players just didn't see UA as "in the spirit" of the game. Power creep had obviously gotten into the works, and though UA worked to pull TSR out of the financial crapper (thanks again to Gary), it did not work for many players of the time. These are those who use everything pre UA, but aren't too fond of things after this point.
Pre 1989 AD&D Players: these are 1e players. Who, in theory reject all or most of 2e, and if they do adopt things from 2e they still claim they are playing 1e.
Post 1989 2e players: these are 2e players
1991 RC Players: I'm not sure how many came into D&D through RC, but lots of basic players took it for what it was an elegant and complete 1 book system for Mentzer style D&D play.
Post 1995 2e players: not even sure who these guys are, as I had quit playing about this time, but this is the era of 2e Options some of which made it into 3e.
The evolvers: many of us followed along in and out of certain categories and even played every edition of the game. We may even have settled on a certain edition, or continue to evolve with the current owner of the IP. I'm sure there are some who have done so--though I know of more who have their particular fondness for a certain era and prefer to stick with that era.
So, who is the "true" D&D player? Well, all of them of course, but for me the answer is a little more specific. None of these categories are fixed, and the borders are amorphous and permeable. But I have strong roots in the 1979 crowd. Even though I started in 1981 playing with Pre '78 players and was taught the game by them, I found myself in the "true believer" crowd of early AD&D pretty hard core. Though I could be said to stretch up into the Pre 1989 crowd, I actually used little of the material post '85.
But having delineated things out to this categorized scale, as useful as such things are or not, the subject isn't quite that simple is it?