Page Six pioneered modern celebrity journalism and restored the neglected art of “gossip” to a proud place in the media lexicon. But nobody knew what to make of it when it first appeared in the New York Post on Jan. 3, 1977.

On a bone-chilling day in the depths of a destructively cold, recession-strapped winter, the first Page Six popped up without warning. It didn’t look like a gossip column — or even a column. It was a boxy, full-page affair that gave no hint as to its author.

The lead story reported that Henry Kissinger was being wooed to become president of CBS. A cryptic cartoon showed Kissinger riding a horse. Page Six was off to the races after that. Its illustrious, 40-years-and-counting run catalyzed a sea-change in the way New York City and America perceived the high-and-mighty — a tableau of raw, exposed egos shorn of spin-doctor defenses.

New York magazine on Aug. 1, 1994, proclaimed Page Six, then led by Richard Johnson, as “New York’s consensus No. 1 column” in terms of “performance, prestige and influence” — and also “the bitchiest.” The judgment would have been just as true in 1977 or in 2017.

Page Six shouldered its way through game-changing media upheavals to emerge as what it’s been since the start: the crown jewel of dramatic, personality-focused journalism that transcends its genre. It bested every rival. It laughed off the 24-hour TV news cycle that supposedly would kill off newspapers, and emerged stronger than ever in the digital age.

Gossip, once a mainstay of popular big-city newspapers, had turned to mush in the mid-1970s. Young reporters after Watergate wanted to chase Pulitzer Prizes, not tipsy supermodels. Bloodless, institutionally focused coverage ruled.

New Yorkers hungered for old-style passion and scandal-wrangling. But aged columnists covered Broadway at a time when theatergoers were afraid to go to Times Square. Others “covered” Hollywood from 3,000 miles away, or filed lists of boldface names who might or might not have actually attended charity fetes.

Page Six put the dazzle back into a city beset by crime and near-bankruptcy. “New money” was swamping Manhattan. Nightcrawlers flocked to mega-disco Studio 54. Page Six conveyed a stirring message: There’s glamour behind the grit, folks! We’re still a sensational town!

The earliest Sixes were churned out in Manhattan Project-like secrecy, two floors above the fourth-floor newsroom at 210 South St. It was edited for all of one day by James Brady before The Post’s new owner, Rupert Murdoch, moved him to New York magazine. (Brady would return for a prolonged stint a few years later.) He was followed by Neal Travis and next by Claudia Cohen, a young, supercharged journo with a neon-bright smile and an instinct for the celebrity jugular.

Page Six put the dazzle back into a city beset by crime and near-bankruptcy.

A later Page Six editor, Susan Mulcahy, observed in her 1988 memoir, “My Lips are Sealed,” that “they don’t teach gossip in journalism school.” Page Sixers had to learn from scratch. They realized you didn’t need to bog down a snarky, 2-inch item with the “official” side of it. “It’s not a problem when you have confidence in your sources,” Travis later told me.

You could write intimately about the human weaknesses of people whose foibles weren’t previously regarded as daily-paper-worthy — models, downtown artists and Wall Street kingpins with squeaky-clean images and mistresses on the side. It wasn’t easy: old-time, Damon Runyon-esque p.r. men were giving way to sophisticated spin doctors backed by phalanxes of lawyers to put up protective shields.

Media moguls made especially juicy subjects. A hapless assistant to Arthur O. Sulzberger, publisher of the stridently pro-gun-control New York Times, let slip to Page Six that her boss kept a loaded revolver in his desk. “Haha, have they fired her, yet?” Post executive editor Roger Wood cackled.

“The original edict for Page Six was money, power and sex,” Wood later said of it — and the “corridors of power.” If a newspaper with its multiple moving parts can resemble a living being, a strong gossip column is its sex gland. Page Six never shrank from pursuing celebrity passions noble and profane.

It could range far from home — it was first to report that “Miracle on the Hudson” hero Capt. Chelsey Sullenberger, not predictable boldfaces like Gwyneth Paltrow, was the star invitee at Vanity Fair’s Oscar party in Hollywood. But it was and is, first and foremost, a New York column.

Page Six put readers on a first-name basis with the Big Apple’s larger-than-life saints and sinners — Leona Helmsley, Donald Trump, Madonna, Rudy Giuliani, Harvey Weinstein, Alec Baldwin, Lindsay Lohan. And who knew that Yankee great Derek Jeter rewarded women he bedded for the night at his Trump World Tower apartment with baskets of autographed baseballs?

Page Six isn’t just sexy, it’s funny. A playful way with words has long delighted readers — from Claudia Cohen’s “They’re breaking out the Valium” at a disaster-stricken film studio to Frank DiGiacomo’s alliterative gems like “fuschia-favoring funkster” for purple-clad Prince.

The column swaggered through seasons of boom and bust. Its subjects evolved with the times — from disco-denizens to celebutantes like Paris Hilton to today’s merry mix of showbiz stars, squabbling politicians, peeved philanthropists, sex-crazed “Real Housewives” and cranky Kardashians.

In an age when online and social-media competition have made all forms of gossip more competitive, Page Six of 2017 remarkably enjoys a much larger profile than it ever did before. It grew from five days a week to seven. By the mid-1990s, it was so formidable that it no longer needed to run on Page 6. It was just as good on Page 8 or 20. The original single page grew to two and sometimes three. Today Page Six is a global brand with its own namesake television show.

Everyone has a favorite story. Among mine: Emily Smith’s March 26, 2013, exclusive that billionaire investor Steven A. Cohen had secretly bought Picasso’s “Le Rêve,” a 1932 painting of the master’s mistress that its previous owner, Steve Wynn, had once infamously torn with an errant elbow. Cohen paid $155 million for it after settling insider-trading lawsuits with the government. The financial, art-world and legal media, all scooped by a “gossip” column!

But I also remember a more mundane item that spoke to Page Six’s deeper quality.

Stranded in Rome for a week after the 9/11 terrorist attacks, I searched the Web for any small sign that New York City would come through. There it was: a Page Six plug for restaurants that were donating food to relief workers “searching for miracle survivors.”

Cheap exploitation! I thought. But then I felt a distinct thrill. Like the knocking at the gate in “Macbeth,” the hype boldly affirmed that back home, the pulses of life already had begun to beat anew.

Life in its untidy, heart-wrenching glory, is what Page Six is about. Look for more tomorrow. And tomorrow and tomorrow.