The 1990s were a dark time for comic book adaptations. When you headed to the theater to check out a comic book movie it was more than a mixed bag. The promise of Tim Burton’s Batman movie gave way to a confluence of terrible sequels, and you’d otherwise have to steer clear of dumb adaptations like Sylvester Stallone’s Judge Dredd, overly grotesque movies like Spawn, or questionably stylized garbage like Dick Tracy or Barb Wire.

Thankfully, when the new decade began, filmmaker Bryan Singer was there to right the cinematic wrongs of traditionally bad comic book movies with X-Men, the long-in-development adaptation of the popular Marvel comic series. Singer’s approach was not too dark but not too light, and he treated the source material with a unique reverence that would eventually inspire the modern comic book blockbuster as we know it.

With Singer’s newest comic book epic, X-Men: Apocalypse — which may or may not be Singer’s last time with the mutants — set to hit theaters, let’s take a look at how Singer managed to define the uber-popular genre.

5. He made the idea of comic book blockbusters a reality.

Sixteen years ago, the Hollywood blockbuster landscape was totally different. Now, the list of the top five highest grossing movies of the year is replete with exceedingly expensive superhero, sci-fi, or animated tentpoles like Star Wars, Jurassic World, Inside Out, and Furious 7, the list for the year X-Men came out is a shocking contrast. Gone are the superheroes, replaced by movies like How the Grinch Stole Christmas, Cast Away, Gladiator, and, weirdly enough, What Women Want, which all beat out X-Men in the highest-grossing year end numbers for 2000.

But change doesn’t happen overnight, and Singer’s relatively small $150 million domestic take led the way for bigger things to come. Singer’s latest X-Men movie, Days of Future Past, made nearly $150 million in its opening weekend. It may be obvious, but simply making a comic book movie, and proving it could be like a big sci-fi event, busted down the door by simply introducing the idea that these kinds of movies could be mega-successful.

4. He helped these movies nail the right tone.

When the lights dimmed for the first X-Men movie, audiences might have been a bit taken aback. Singer opened his movie about mutants with superpowers with a 1944-set sequence of a young Magneto separated from his parents being sent off to a concentration camp while revealing his powers in the process. The Holocaust is not the first thing you’d think of when you want to watch a superhero movie, but the serious-minded themes of the opening and the popcorn-style action humor that followed maintained an expert tonal balance that is still being copied today.

Throughout the entertainment-focused highs of the Marvel Cinematic Universe and the grimdark lows of Batman v Superman: Dawn of Justice, filmmakers continually wrestle with replicating the inherent comic book fun with potent subtext Singer captured, and it was something he is still well aware of. He told Collider that until X-Men, comic book movies were simply farcical nonsense like Batman and Robin, “Comic book movies had died, there was no concept of one as anything but camp. I took it on because I saw the thematics of it were interesting to me.”

3. He figured out how to perfectly balance the source material and original ideas

Approaching any adaptation is difficult whether you’re making a small indie movie version of classic literature or a $200 million comic book movie. The question is, how beholden are you to the source material versus how much do you want to stray from it to make it your own vision? Comic book movies have the added threat of fandom ready to pounce on every single decision you make whether it’s outfitting your heroes in leather suits to questionable casting decisions. Singer realized throughout his X-Men tenure that you need a simple give-and-take.

The first X-Men movie wasn’t based on any particular comic book storyline, which was fine because it was still new territory and it had to be an introductory movie anyway. X2 took its cues from Marvel’s “God Loves, Man Kills” source material, and by the time he got to his third X-outing Singer just outright called it the same thing as the comic: “Days of Future Past.” Singer knew that you at least have to give a tip of the hat to the thing that inspired all these multi-billion dollar properties, but you can’t hope to replicate them shot for shot a la Watchmen. They’re two mediums that have to meet somewhere in between.

2. He reasoned that comic book movies should go big, but stay small.

Comic books are ancient myths made modern. They tell enormous stories of inhuman individuals trying to figure out what it means to be human. They have scale, they have weight, and they have a scope that could get out of hand if a filmmaker doesn’t realize that it isn’t size that matters. Singer’s X-Men movies, and even Superman Returns, are about the individuals that grapple with gigantic, other-wordly problems. They’re small people caught up in a huge CGI-filled spectacle.

Singer himself has wavered from this in Days of Future Past, and maybe Apocalypse, but he’s still much more primarily focused on dealing with the actions of the characters, which is something that has made the MCU has used to make itself into something a bit more than just eye candy. Brett Ratner’s bloated X-Men: The Last Stand or Sam Raimi’s studio-inflated Spider-Man 3 got too far away from this, but the good ones still take their cues from Singer.

1. He made them a legitimate destination for actors and directors alike.

Richard Donner’s Superman is kind of like the grandfather of this idea. Cast Marlon Brando in your superhero movie and it immediately gives it some heft. Cast two well-loved Shakespearean trained actors like Ian McKellan and Patrick Stewart in your superhero movie and it does you one better. By bringing this refined and respectable concept to an otherwise loopy story, superhero movies were no longer seen as a second-tier territory. They could now be thought of as films where actors could flex their skills and be a little melodramatic in the process. Singer’s approach is why you see celebrated actors like Benedict Cumberbatch, Tilda Swinton, Natalie Portman, and more take the comic book plunge.