The first time I ever saw “Night of the Living Dead,” the low-budget masterpiece of flesh-eating midnight terror directed by George A. Romero, who died on Sunday, it was in 1974. I was at home on a lonely high-school Saturday night watching TV, and at 11:30 p.m. an oddball black-and-white movie that opened in a cemetery just kind of…appeared.

I knew absolutely nothing about it. At that point, low-budget horror films — even those that became notorious and sold a lot of tickets on the drive-in and grindhouse circuit, as “Night of the Living Dead” had — possessed an up-from-the-underground, not-quite-on-the-radar quality. They weren’t all that easy to find (especially if you were 15). Yet here was “Night of the Living Dead” on TV. As I sat there in the darkened living room, the film’s end-of-the-world atmosphere of rapacious anxiety seemed, at that moment, as if it had been fashioned for the small screen, and made just for me. It was almost as if the regular programming — the banality of the usual mainstream diversion — had been suspended, all for this news bulletin from a zone beyond the Twilight Zone.

The images had a high-intensity lurid starkness that looked like something out of a silent film crossed with something out of a documentary. The bespectacled creepy geek who said “They’re coming to get you, Barbara!” seemed to be teasing not just his poor sister but anyone who was watching the movie. Who, exactly, was coming to get us? In a minute or so, we found out.

The film’s first zombie, wordless and relentless, reminded me of Frankenstein’s monster, only it was like seeing Boris Karloff on homicidal overdrive. He kept coming, hard and fast, banging his open hand on the car window like he wanted to smash through it. He was scarcely a “character” at all; he was all id and violence and drive, all rampaging hunger. He arrived so quickly and relentlessly — out of where? out of nowhere — that his presence burned through the hidden niceties of every horror film I’d ever seen. (Even the first attack by Norman Bates, in the motel shower, had been prepared for. It had been built up to.) The movie had barely started, yet this monster was already at the climax of his rampage. The effect wasn’t just scary — it was insane. As I sat there, spellbound with fear, the artistry of George A. Romero seemed to be crushing the entire world around it.

The cemetery scene was, of course, the ghoulish appetizer for a movie that would take the possibilities of flesh-ripping, intestine-eating gore to frenzied new heights of mayhem — or depths of depravity, depending on your vantage. When “Night of the Living Dead” was first released, in October 1968, the press was scarcely ready for it. The movie was dismissed, by and large, as a grotesquely amoral stunt — something beneath an actual motion picture. Variety, for one, wrote that the movie raised “doubts about the future of the regional cinema movement and about the moral health of film goers who cheerfully opt for this unrelieved orgy of sadism.”

“Rosemary’s Baby,” released earlier the same year, was also a work of shivery disturbance, yet it was also, quite obviously, a movie of high cinematic elegance (it established Roman Polanski as the successor to Hitchcock). “Night of the Living Dead,” by contrast, seemed to be trashing the very essence of what a motion picture was. And in a way, that view of it wasn’t entirely wrong. What the movie was doing, from the low end of the exploitation spectrum, was revolutionizing cinema, opening up the possibilities of horror — not just the gruesome sensations of it, but the meanings of it — in much the same way that the film’s zombies ripped open those bodies.

It’s worth recalling that George A. Romero didn’t invent “the zombie.” The notion of an undead creature stalking civilization in a hellish trance, with the popped eyes and outstretched arms of a brain-dead demon, emerged from Haitian folklore; it’s an element of voodoo mythology that dates back several hundred years. The concept wasn’t introduced to Western culture until the late 1920s, and there’s one early zombie movie that remains a haunting work of cinematic art: the Val Lewton/Jacques Tourneur 1943 classic of forbidden island sensuality, “I Walked With a Zombie.” It’s a dark poem of spectral terror.

What Romero did in “Night of the Living Dead” was to reinvent zombies by stripping them of almost every quality but aggression. He turned them into ravenous lurching cannibals who made up in appetite what they’d lost in consciousness. And it was the aggression — the sheer reptile-brained, flesh-chomping spectacle of it — that proved revelatory.

After the early wave of condemnation, “Night of the Living Dead” began to be recognized as a live-wire nightmare on film (the movie’s latent champions included Pauline Kael and Rex Reed), and a collective case was made for its resonance as a piece of primal social commentary. The film was often said to be a statement about the Vietnam War — about the atrocities that were being committed there — and in 1968, you couldn’t get much more serious than that. As much as it came into the world as the ultimate garish B-movie, it didn’t take long for “Night of the Living Dead” to acquire a reputation as a work of visionary horror.

I buy the charged relevance — to a point. Whatever it was that possessed Romero, a 28-year-old Pittsburgh-based director of industrial films and commercials, to cobble together $114,000 to make the most outlandishly crazy-gross-scary film that anyone had ever dared dream up, I don’t think the movie would have erupted out of him in the way that it did had it not been for the presence of the living-room war and the other upheavals of the late ’60s. Romero, as anyone who ever met him can attest (I had the pleasure once, in college), was a low-key mensch and gentleman: the least obsessive director of outré horror you could imagine. I totally believe that he thought he was making “responsible” films.

Yet there’s an ominous free-floating vagueness to the metaphorical scheme of “Night of the Living Dead,” and that’s part of its power. It channels the cosmic breakdown that was 1968. Romero knew how to understate a statement. That’s why he had the forward-thinking audacity to make a horror movie where the hero, played by Duane Jones, is black yet his race is never mentioned. (The famous final scene might be the cinema’s first commentary on the relationship between African-Americans and the police.)

It’s one of the grand ironies of movie history that after the original disreputability of “Night of the Living Dead,” the notion of the-living-dead-as-metaphor evolved into a kneejerk kind of rarefied critical/fanboy gospel, one that cast its shadow over the entire zombie genre. What kicked it up to major levels, of course, was Romero’s second great zombie movie, “Dawn of the Dead” (1978), a sequel done in deluxe candy-apple color, and as fully conscious of what it was up to as “Night of the Living Dead,” a decade earlier, had been only semi-conscious.

“Dawn” was set in a shopping mall, and that sprawling temple of what then seemed the ultimate in gaudy consumerism — if only the zombies had a hint of what was to come in the age of Amazon and PayPal! — became a kind of movie-set-as-metaphor. “Dawn of the Dead” was a kicky action splatterfest, with Romero’s special-effects wizard, Tom Savini, taking on a biker role that showcased the new era of Fangoria superstardom. But it was really all about the shopping, man! As the film’s hero said, in the film’s most irresistibly over-explicit line, “They’re us, that’s all.”

The zombies, that is. And they were. Skulking through those stores. Yet when you look at the legacy of the zombie culture that George A. Romero created — when you look at “28 Days Later” and its sequel, or “The Walking Dead,” or “World War Z,” or “Shaun of the Dead,” or Romero’s own later zombie entries (“Day of the Dead,” etc.), or a hundred other zombie-knockoff fright films — the real metaphor isn’t about Vietnam, or “capitalism,” or disease, or anything else that you can stuff into a fortune cookie. It’s about something more basic but ethereal, something that you can sense without putting it into words: the hidden aggression we all feel deep down, as the price of too much civilization.

Romero, in a hardscrabble, mostly outside-the-industry career, made a number of other films, a handful of them pretty good, like “Martin” (1978), the story of a kid who wants to be a vampire (but has to rely on syringes rather than fangs), or “Knightriders” (1981), his drama of outlaw biker culture in King Arthur drag, or “Creepshow” (1982), the enjoyably old-school neo-EC Comics anthology film he did in collaboration with Stephen King. Yet Romero never stopped returning to the living dead. Maybe those were the filmmaking opportunities that presented themselves to him, but he also kept the zombie fever alive in his blood. The zombies that sprung from his imagination are now part of our imagination. After all these years of rising and chomping, they’re still a threat, a contagion, and an electrifying device of dramatic horror, but more than that they’re a warning: This is what it looks like when we forget who we are.