I'd go with RuneQuest over Call of Cthulhu. Call might have had more staying power, but the BRP system originates in RuneQuest.
I think RuneQuest was also the first game to have mechanical weight given to in-game social constructs, primarily Cults. Characters were expected to be members of a cult dedicated to one god, and different cults had access to different Battle Magic and Rune Magic, and wanted you to do different stuff and emphasize different skills. And if you were strong and dedicated enough, you could become a Rune Lord which was a significant power upgrade.
Ryan Dancey is one of few figures who had a major influence on the overall TTRPG world without themselves primarily being a designer (I'm not sure, but I think the only game design credit he has is Hero Builder's Guidebook, which was basically an early D&D 3.0 book about how to realize certain character concepts using that system). In most cases, you start with a game designer who then starts a company because that's how they can get their game created and sold, and if they happen to be good at the business side that's a (rare) bonus.But I am always happy to say that Ryan Dancey is one of the most important figures in the ttrpg space, which feels to me to be a weirdly minority position. I think the 3E SRD and the OGL may be one of the most important inflection points in the history of the industry -- moreso than probably 99% of the games mentioned in this thread.
I've definitely seen similar mechanics in other games, though rarely expressed as opposed pairs. Ars Magica had both "regular" personality traits which you could use to determine behavior, and Passions you could use to get mechanical benefits when acting in accordance with them (the latter required taking the appropriate Virtue though). GURPS had lots of disadvantages that were personality traits, which usually required a Will check to act against them (4e changed that to a fixed value instead).Did the personality traits, Virtues and Vices, such as merciful/cruel, proud/pious, valorous/cowardly, etc., etc. have any influence on other games? It's the earliest game I can think of where players rolled to determine how their character might react to a situation.