It's probably not controversial to say that the Dungeons & Dragons game from 1974 was the most important and influential game in the whole genealogy of all RPGs. Every game that followed was either an attempt to make a game that improves on D&D or make a game that is different from D&D. They were either a direct response to D&D, or expanded on a game system that was.
The real question is, what other games can be considered hugely influential on how people design game systems today?
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.