Kumail Najiani has to be living the dream right now. The actor/writer/comedian is a pretty obvious huge nerd, and he's on the verge of starring a big comic book movie. He'll be part of the ensemble cast of Marvel's The Eternals next year, but that doesn't mean he's gone all in on The Eternals as the greatest comic books ever. When recently asked what he thought the most influential comic book of all time was, he didn't even name a Marvel book.
I think Watchmen is probably the most influential comic book that there has been. He changed the way that people looked at superheroes, really got into the psyche of them.
Kumail Nanjiani's opinion here is going to be one that's shared by a lot of people. Even if you don't believe Alan Moore's Watchmen is the most influential comic, it's difficult not to put it near the top of the list. As Nanjiani says, it took a different angle to exploring superheros in comics that most people had never seen before. It also was one of the comics that propelled the "dark and gritty" comic aesthetic that would become a predominant part of the medium for the next decade, and has never truly gone away entirely.
There are certainly a few other options for majorly influential comic books. Action Comics #1, the first appearance of Superman, can't be overlooked as the entire comic book superhero boom can be traced back to that. It's even an influential book within the world of the Watchmen graphic novel, a catalyst for the events of that story as well as the existence of the book of the first place.
Frank Miller's The Dark Knight Returns shares a lot of elements with Watchmen and thus is equally responsible for many of things Watchmen accomplished, and it actually predates Alan Moore's book by a few months, so many might consider that the real influence.
I mean, let's be honest, if Kumail Nanjiani had tried to drop The Eternals into this conversation we'd know he was messing with us. The Eternals aren't even massively popular characters among many serious comic book fans. Of course, the same was once said about the Guardians of the Galaxy, and that turned out pretty well.
Originally planned for release in November, The Eternals has been pushed back to an early 2021 release to make room for Black Widow, which took The Eternals original release date after Widow was delayed due to theater closures. The Eternals arrives February 12, 2021