Warhammer and MechWarrior for miniature combat for me. They also helped me understand how to be a DM for pen and paper games on what was possible and what was just pure fantasy.

Traveller and Apocalypse World would be my two top picks.

I've been thinking recently about what huge an impact Apocalypse World had. I think it's never actually been very popular as a game that is being played and I've seen plenty of people having major issues with that. It's probably become overshadowed in those regard by ots descendant Blades in the Dark. But this whole branch of the RPG genealogy is called Powered by the Apocalypse for a reason, and I do still see it referenced in passing when it comes to discuasions about developments in game design. It certainly was the mosy eye-opening game I ever read, opening up completely new perspectives of what RPGs could be.

It could depend on which game systems are more famous in your country. Games like Call of Cthulhu and Runequest , both using BRP (a percentile system) were very famous and played in Spain for many years in direct competition of Dungeons & Dragons.

In my very own opinion the RPGs can be crudely divided into 5 or six generations or stages (with a lot of overlap and finicky stuff) depending on some "development" or "evolution" in rules sets and gaming styles.

1. The first and foremost is of course D&D that kind of set the scene and more or less created the hobby. There may be others that had the same idea, but this one was the one who gained traction. I would characterize this system as one with Levels and most character development happening after game starts. Fast up, easy to to handle character getting better. (Although Rolemaster belongs to that generation too and makes nothing easy).
2. The second generation happened almost directly after with Runequest and Traveller as surviving examples. Level is removed and there is some work on the character before play, Traveller even removes most of the character development after game starts (which is to me the apparent reason the game never have expanded outside a very fanatic core (I include myself in that core). Characters is still generated randomly with dice rolls etc.
3. After some lull the third generation comes around with GURPS and HERO (Champion) as giants, here you have absolute control of the character generation and the game is no longer fixed to a specific franchise. The players of these games are less often first timers and newbies as much as veterans longing for freedom and exploring new worlds of variants and exotica.
4. Here comes the (in my opinion biggest change since the first generation) and that is the Storyteller system, what was so impactful was not so much the system, as the defocus from the system and instead started to looking at the generation of a story together (but still under the eye of a gamemaster, eh, Storyteller). The dots on your character sheet was just one part of the character, the prelude and the relations with NPC as well as PC was as (if not more) important. Character development was not any longer limited to increasing number on your stat, your relationship to the world and your role and place was more important. Sure, you have 5 dots in potence, but that don't matter when the Prince hates you.
5. (and perhaps 6) here things starts to get a bit muddled, but I think that the things that came out of The Forge with Fate and PbtA as cases in point, with the game throwing of the chains of fixed attributes (Fate) and redefining the gamemaster (PbtA) as two clear examples of what changed.

... ehe, slightly more than two cents of opinions ...

You could argue that Chainmail <- clicking this link apparently force redirects to the armor, sorry about that. or Siege of Bodenburg were extremely influential in their own right.

If we talk about introducing people to RPGs in general, it's hard to beat Call of Cthulhu. IIRC in Japan it's more popular than D&D and this has spilled over into China. The top three RPGs in China are D&D, Call of Cthulhu, and Fate and in a surprising number of cases game peripherals (like dice, dice towers, dice trays, GM screens, etc.) are sold as aids for Call of Cthulhu on Taobao, the country's premiere online shopping system.