If there’s a word in American life that should probably be retired (or at least used a lot less often), it’s “rebel.” Back in the ’50s, when Marlon Brando was rebelling against “whatever ya got,” the rebel was a rare breed. But the rock revolution opened the door to a generation of rebels — the freak-flag-flying music stars, plus their armies of followers. The hippies and yippies were rebels. So were the glam rockers, punks, disco divas, and rappers, not to mention the raging antiheroes of New Hollywood films like “Bonnie and Clyde” and “M*A*S*H” and “One Flew Over the Cuckoo’s Nest.” By the time the director Ivan Reitman came along in the late ’70s, it seemed like there wasn’t much left to rebel against — at least, not in middle-class American life. But that’s where Reitman, who died Saturday at 75, had an inspiration.

What if rebellion as we knew it really was played out? After the moralistic fervor of the ’60s and ’70s, what if there was nothing left to the idea of a “counterculture” but the sheer scruffy joy of bad behavior? What if the rebel no longer stood for anything but himself?

In 1978, when Reitman, a television, theater, and low-budget horror producer from Toronto, launched his Hollywood career by producing “National Lampoon’s Animal House,” the world was ripe for a new breed of rebel, the kind who didn’t take anything he stood for seriously. It was also ripe for the kind of rebellion that looked like you could have a blast doing it.

“Animal House” represented the collision of a shaggy mélange of talents: Doug Kenney and Chris Miller, from the National Lampoon (the film was based on Miller’s outrageous short-story reminiscences of going to Dartmouth); Harold Ramis, a refugee from “SCTV”; the director John Landis, who had helmed “The Kentucky Fried Movie” (the first film from the “Airplane!” team); and, of course, a cast that featured John Belushi, who as Bluto became the film’s iconic, anarchic, food-fight-happy id.

From the outset, though, it was Reitman’s gut-busting impulse to take the ribald, semi-underground naughtiness of the Lampoon and pour it into something new: a slob comedy for mainstream audiences. The key to “Animal House” is that its heroes were frat-house louts and losers and layabouts who wanted nothing out of life but the right to party. That’s all they stood for. Yet they were going to have to fight for that right. And “Animal House,” in elevating toga parties and frat high jinks to a higher form of debased hilarity, flipped the very idea of rebellion on its head.

The movie had a seismic influence on the culture. It made frat houses hip (they’d been fading for years), and the fraternity came roaring back to the center of college life. But the extraordinary thing that “Animal House” did was to purge rebellion of everything but sex, drugs, and rock ‘n’ roll — or, in the case of Bluto, sheer mayhem. The movie cruised along on a template of hedonism that has never left us — you can draw a direct line from “Animal House” to the bacchanal dreams of “MTV Spring Break” to “Jersey Shore” to the binge-drinking-and Tinder-hook-up decadence of today. This was a rebellion that preened, that caroused, that had no shame. The only thing it was trying to overthrow was any vestige of respectability.

After “Animal House” put Reitman on the map, he wasted no time transitioning into the role of director, making a trio of films that redefined American comedy. It’s no coincidence that all three starred Bill Murray. In Murray, Reitman found his muse, his antic lazy-bones hero, his ironic anti-rebel. And Reitman, as a filmmaker, turned out to be have a blockbuster broadness infused with a human touch. His movies weren’t subversive, exactly, but they had spirit and sass, thumbing their noses at the status quo.

The first of them, “Meatballs,” came out in 1979, and it was the scruffiest of summer comedies — a low-budget throwaway, produced in Canada, in which Murray played the world’s most disreputable camp counselor. The movie was a sleeper hit that almost singlehandedly launched the tawdry genre of ’80s summer-camp comedies (skewered to perfection in “Wet Hot American Summer”), most of which were rated R and did their best to be titillating. “Meatballs” was rated PG and revolved around Murray’s attempt to cheer up a despondent camper. Yet it was the first comedy to showcase the Murray Attitude — the snark, the what-the-hell detachment, the total abandonment of responsibility presented as a higher value. In the film’s most famous scene, Murray gives a pep talk to his campers, telling them that if they’re worried about beating their rival camp in an upcoming olympiad, they shouldn’t be, because “It just doesn’t matter!” In a goofy way, he and Reitman were undercutting a century of movie nobility.

But “Meatballs” was merely the appetizer. “Stripes,” Reitman’s 1981 follow-up, was a military jape that showcased Murray at his most gloriously unhinged; it was like “M*A*S*H” updated to the age of round-the-clock mockery. Murray, leading his fellow soldiers in basic-training choruses of Manfred Mann’s “Do Wah Diddy Diddy,” was the most blissfully cockeyed of troublemakers. All of which set the stage for what may be the defining laughfest of the 1980s.

Ghostbusters” was comedy on a grand scale: a gooey special-effects movie that skewered the whole idea that it was a gooey special-effects movie. Murray was the main Ghostbuster, but really, he seemed to be inside the movie and outside it at the same time, doing a running commentary on the absurdity of everything that was happening. Released in 1984, “Ghostbusters” was the quintessential comedy of the Reagan age, because it presented the ghosts as this awesome threat…which turned out to be a complete joke, which mirrored the slight unreality of the era. Reitman had now taken the snarky, nattering American rebel and given him an entire movie to skewer. And that’s exactly what Murray did. He bestrode “Ghostbusters” like a hipster Groucho even as he was popping the movie like a balloon.

Reitman must have known that he couldn’t top “Ghostbusters,” not with its beloved Stay Puft Marshmallow Man climax, and he didn’t really try (though he did churn out the misbegotten “Ghostbusters II” five years later). Even so, it took a while for Reitman to refocus his career. He directed the drab comedy-action-thriller “Legal Eagles” (1986), followed by two movies that were the quintessence of what made high-concept comedy annoying: “Twins” (1988), which teamed Arnold Schwarzenegger and Danny DeVito, and “Kindergarten Cop” (1990) which teamed Schwarzenegger and a roomful of school kids. But “Dave” (1993), starring Kevin Kline as a presidential look-alike who is tapped to be the stand-in for the Chief Executive, had an old-fashioned élan, and Reitman rediscovered his audacity as a producer when he got the cracked idea to make a movie out of Howard Stern’s “Private Parts” starring Stern himself. The film’s biopic-of-Howard stuff is banal, but when it turns into the war over words between Stern and his WNBC overlord (the role that established Paul Giamatti), “Private Parts” has an exuberant prankishness.

“Animal House” aside, the most influential thing Reitman did as a producer, apart from producing his gifted filmmaker son Jason Reitman (“Up in the Air”), who recently carried on his father’s legacy with the successful reboot “Ghostbusters: Afterlife,” was to shepherd the career of Todd Phillips (“Joker”). Phillips was at the Sundance Film Festival in 1998 with the controversial documentary “Frat House” when he spied Reitman, whom he’d never met, and pitched him out of the blue on his idea for “Road Trip” — a movie directly inspired by the spirit of Reitman’s ’70s and ’80s comedies. Reitman bit, and two years later “Road Trip” became Phillips’ first feature, with Reitman serving as executive producer. What Phillips was talking about was the frowzy clown-rebel spirit that Reitman had perfected, a spirit you can see ricocheting through Phillips’ own movies, from “Road Trip” through the “Hangover” films right up through “Joker.” That’s the era that Ivan Reitman defined, reveling in the scruffy hilarity of rebels who stood for nothing beyond themselves, even if you could hardly imagine them outside a studio blockbuster.