While these books sound interesting, “amazing and incredibly influential achievement” sounds more like something someone might say about a President than a sci-fi author.
Larry Niven's most famous work Ringworld, inspired both of the massively popular games Magic the Gathering, and Halo: Combat Evolved.
I suspect that Niven and Fillmore have roughly equal name recognition, though, simply by the nature that Niven is still alive, and appears to be more consequential long term.
While Larry Niven is most famous for his hard science fiction, in the traditional sense of the term, he also has a fantasy universe, with a decent introduction at https://en.wikipedia.org/wiki/The_Magic_Goes_Away In this universe, magic is a finite quantity, which gets used up. The modern world is mundane not because magic is impossible, but because it was all used up.
(It would be interesting if he ever wrote the story set in this universe, after the modern times, in which humanity gets out to space, and, uh, hey guyz, magic kinda... works out here... what the heck? It wouldn't necessarily take long to figure out what the deal is with Earth being a dead zone, but it would cause some interesting political upheaval as suddenly the sparse space colonies that nobody thought were worth anything and barely even worth the effort became industrial powerhouses as the only place where magic works... and not just the tame, dying magic of Niven's stories, but the original wild, abundant magic the stories claimed Earth initially had.)
Likely more people (inside the US and outside too) are more familiar with Fillmore St. in San Francisco[1], which is named for President Fillmore, and its famous theater / music venue of the same name.
