The tale I'm about to tell is an ancient one, passed down through the ages. It tells of heroes, villains, and even you, fair user.
In the beginning, there were wargames. Though now the only of their number of any note is Warhammer 40k, for a time they were rulers in their own right.
One day however, a group of nerds wondered
>what would it be like to play as warrior from the battalion they commanded?
Thus, the very first RPG was born: Chainmail.
Chainmail was a very different game from the RPGs that you know today. Some would hardly recognize it as an RPG at all, but it was a start. In time fantastical elements were added, and it came to be called Dungeons and Dragons.
Compared to the modern incarnation this game was almost comically simplistic. All weapons only dealt 1d6 of damage (because d6s were the only dice they had), and wizards had but a single spell. Additionally, fantasy, pulp adventure and science fiction elements were freely mixed, owing to the lack of hard genre lines during the time period.
This game grew stronger and more popular. Other games from other companies followed, some simply copying D&D, others going off in new directions. A brand new hobby was taking root and growing, and D&D was about to push it even farther.
Enter Advanced Dungeons and Dragons. This is the system that most old timers started with. It added unprecedented complexity to D&D, allowing options that had never before been seen. Rules were fleshed out, and the rulebooks hired professional artists to illustrate, rather than throwing some mechanical pencils at an intern and telling them to get drawing.
Contrary to OD&D, there was now a hard, presumed setting (Greyhawk), and the rules made assumptions and gave explanations about the setting. It was a renaissance for tabletop RPGs.
Despite the seemingly sunny skies, a storm loomed. Beyond the horizon, problems were brewing.