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Steve Dunleavy visits the American Cemetery in Colleveill near Omaha Beach along the coast of Normandy in 2003.

Steve Dunleavy sitting at the end of the bar at Langan's on its last day open for business on Jan. 18, 2018

Steve Dunleavy, the hard-hitting, hard-drinking journalist who helped define The New York Post as a crime reporter, editor and premier columnist, died Monday at his home on Long Island. He was 81.

The cause was unknown.

“Steve Dunleavy was one of the greatest reporters of all time,” said Rupert Murdoch, owner of The Post.

“Whether competing with his own father in the famous Sydney, Australia, tabloid wars, or over the last 40 years in New York, Steve’s life story is littered with great scoops. He was much loved by both his colleagues and editors.”

“His passing is the end of a great era,” Murdoch added.

Over the course of his epic career, Dunleavy scored countless exclusives, including interviews with the mother of Sirhan Sirhan, Robert F. Kennedy’s assassin, and confessed “Boston Strangler” Albert DeSalvo. The rapist also posed in the nude for Dunleavy, who had smuggled a camera into prison for the story.

Dunleavy also flew to California to entice three members of Elvis Presley’s “Memphis Mafia” bodyguards to reveal the singer’s drug addiction.

The ensuing series of stories boosted the circulation of the Star tabloid, where Dunleavy was then working, from 2 million to 3 million, and also led to the publication of a best-selling book, “Elvis: What Happened?” shortly before Presley’s death.

Fans of the King responded with death threats that followed Dunleavy to The Post — where someone even sent a hearse with instructions to pick up his body.

That tale is one of many inspired by the legendary newsman, many of which start in a tavern.

Perhaps the most memorable involves a snowy night at the Upper East Side media hangout Elaine’s, where Dunleavy met the Norwegian fiancée of an Australian journalist.

While his pals decamped to another bar across the street, Dunleavy and the fiancée wound up outside, “humping in the snow, arses going up and down,” former Daily Mail correspondent George Gordon told The New Yorker for a profile of Dunleavy in 2000.

“As we were watching, a snowplow came up the street and ran over Dunleavy’s foot,” Gordon said.

“By this time, the entire bar was in uproarious laughter.”

Dunleavy “was so loaded, it didn’t matter,” Gordon said, but was eventually taken by ambulance to a hospital, where he was diagnosed with a broken foot.

Upon learning of the incident, rival journalist Pete Hamill bitterly sniped, “I hope it wasn’t his writing foot.”

Another incident at Elaine’s ended with Dunleavy socking since-disgraced record producer Phil Spector in the nose — one of many brawls sparked by liquid courage.

“Countless fights, yes, but alas, not a good won/loss record,” Dunleavy once lamented.

Veteran Post columnist Steve Cuozzo recalled the time Dunleavy phoned the newsroom on a Saturday morning and told the assistant who answered, “Mate, this is Dunleavy. Take down this number.”

After reciting the digits, Dunleavy had the assistant repeat them to him.

“Great. Now call me back and tell me where I am,” Dunleavy replied.

Dunleavy also came up with a snappy comeback when The Post was pilloried at the time for the now-classic Page 1 headline, “HEADLESS BODY IN TOPLESS BAR,” Cuozzo recalled.

“What should we have said?” Dunleavy wondered.

‘Decapitated cerebellum in tavern of ill repute?’”

A second-generation journalist and native of Australia, Dunleavy quit school at 14 and began working as a copy boy at The Sun, a Sydney tabloid that employed his dad as a photographer.

He left the paper for the rival Daily Mirror and was made a cub reporter, eventually proving the extent of his competitiveness by slashing the tires on his father’s car when they were both covering a story about a group of lost hikers.

Dunleavy claimed not to know who owned the car, but the older man got his revenge when they were both chasing a story about a criminal dubbed the “Kingsgrove Slasher.”

When Dunleavy found a laundry room where he thought the Slasher was hiding, he went in, hoping “to catch him single-handedly” — only to hear a dead-bolt snap behind him.

“My father had locked me in. I was trapped for hours,” Dunleavy told The New Yorker.

“When I got out, I went home and said, ‘Dad, you could have got me fired.’ He said, ‘Remember the Blue Mountains.’ ”

Dunleavy left Australia for a job with the South China Morning Post in Hong Kong, then freelanced his way across Asia and Europe before winding up in London, working on the city’s Fleet Street for the United Press International wire service.

Dunleavy later “fooled around” in the Bahamas before heading to New York, where he claimed to have arrived on Dec. 28, 1966, with seven dollars in his pocket.

He lived in coffee shops for a week before landing a job with UPI, which led to him meeting fellow Aussie and News Corp founder Murdoch, whose American correspondents had offices in the same building.

Murdoch hired Dunleavy in 1967 to write stories for his papers in Australia and Britain, then tapped him as news editor of the National Star tabloid, which Murdoch launched in 1974.

At the Star, Dunleavy also wrote a column titled “This I Believe” that so impressed the far-right John Birch Society that it named him its “American of the Year” — despite the fact that he wasn’t a citizen.

Dunleavy continued the column after becoming The Post’s top crime reporter when Murdoch bought the paper in 1976.

He soon launched into coverage of the “Son of Sam” murders. Dunleavy’s ingenuity included dressing in what looked like scrubs to sneak into a hospital and interview a victim’s family.

“I lost count of the number of times I posed as a cop, a public servant or a funeral director,” Dunleavy told writer William Shawcross, author of a 1993 Murdoch biography.

In 1986, Murdoch made Dunleavy one of the first reporters for “A Current Affair,” a tabloid-style TV program produced for Murdoch’s then-fledgling Fox broadcast TV network.

During nearly a decade with the show, Dunleavy beat ABC’s “Nightline” out of an exclusive interview with Jessica Hahn, the mistress of televangelist Jim Bakker, by going to her house and telling an ABC driver that Hahn had been taken to a hospital.

Dunleavy’s blanket coverage of Amy Fisher’s shooting of Mary Jo Buttafuoco — amid Fisher’s affair with Mary Jo’’s husband, Joey Buttafuoco — also led The New Yorker to say that story “at times, appeared to run exclusively on Fox.”

When Dunleavy was let go in a shake-up shortly before “A Current Affair” was canceled, he returned to The Post, becoming a columnist who crusaded against liberal politicians and celebrities, while championing members of the NYPD and FDNY.

“You walk under the portals of One Police Plaza, and above are the etched names of 713 cops who have fallen in the line of duty protecting this city,” he once wrote.

“Turn to your right, and then to your left, and you are surrounded by heroes. It makes someone like myself feel very small.”

Former top cop Ray Kelly on Monday described Dunleavy as “a diehard supporter of the NYPD, particularly street cops.”

“As someone so deeply knowledgeable about the city, he knew how difficult and demanding the job is,” Kelly said.

When The Post moved from its offices on South Street to its current headquarters in Midtown, Dunleavy routinely spent his afternoons across the street at the since-shuttered Langan’s bar, conducting interviews and taking calls from editors.

His failing health led him to retire from The Post in 2008, when he was feted with a blowout party.

In an interview tied to his retirement, Dunleavy told The New York Times, “I always had dreams of dying at the desk.”

“It’s frustrating not doing what I love best, and serving — I know it sounds corny — the one who I admire the most. Murdoch. The Boss,” he said.

In 2017, he was inducted into the Australian Media Hall of Fame, which lauded his “rambunctious, swashbuckling and hard-drinking career” and said he “earned the term ‘legendary reporter’ through his whatever-it-takes, larger-than-life approach to journalism.”

Dunleavy is survived by his wife, Gloria, and their sons, Peter and Sean.

Additional reporting by Keith J. Kelly