It’s a legend that even now, 20 years after Jerome Robbins’ death, threatens to define him: While berating his actors, he stepped farther and farther back on stage until he toppled into the orchestra pit.

And no one said a word to stop him.

Some say the show was “Call Me Madam,” “High Button Shoes” or “Billion Dollar Baby.” (An eyewitness tells The Post it was, in fact, “West Side Story.”) But the underlying message is the same: The choreographer and director was a terror to work with. Last month, after a “Chicago” actor killed himself following what was reportedly a brutish rehearsal, many recalled Robbins and his penchant for pushing dancers and actors to the breaking point.

Still, it’s hard to imagine Broadway or the ballet without him. Which is why Robbins — who was born 100 years ago and died at 79 on July 29, 1998 — is as revered as he is reviled. His centennial year is being celebrated across the country and in Germany, France and the Netherlands. On Aug. 9, there will be a tribute aboard the Intrepid in Manhattan, with performances and panels moderated by Robbins biographer Amanda Vaill.

In ballets and such musicals as “West Side Story,” “Peter Pan,” “The King and I” and “Fiddler on the Roof,” Robbins brought a naturalism to dance and movement that was revolutionary — reason enough why those who survived both him and his wrath tend to recall the master, not the monster.

“Stephen Sondheim said that Robbins was the only genius he’s ever known,” said Vaill, who had access to the director’s diaries and papers while writing 2006’s “Somewhere: The Life of Jerome Robbins.”

And he was, she points out, self-taught: Unable to afford more than a year at NYU, young Jerome Rabinowitz dropped out and ferried between Weehawken, NJ — where his father urged him to join the family corset business — and New York, where he kick-started his dance career.

Along the way, he developed what Vaill calls “a kind of tunnel vision — once he’d seen what he wanted, nothing else was important.” In the name of art, he’d make actors and dancers go through their paces again and again, often screaming at them and hurling insults.

“Jerry not only attacked you, he attacked your family, your background, where you lived, how you lived, who you studied with,” Tony Mordente, a “West Side Story” cast member, told biographer Greg Lawrence.

Yet Mordente and many other stars say they owe their careers to him.

“The extreme conflict between his admirers and disparagers made my book an emotional ordeal to write,” Lawrence told The Post of his 2001 biography, “Dance with Demons: The Life of Jerome Robbins.”

A perfectionist, Robbins was even hard on his collaborators, including “West Side Story” composer Leonard Bernstein.

“My father had to struggle with so many aspects of Jerry’s challenging personality,” Bernstein’s daughter, Jamie, told The Post. “He was rude and imperious and harsh and awful to artists . . . and yet my father managed to set it aside and go on working with Jerry.”

But others never forgave him — if not for his cruelty, than for naming names before the House Un-American Activities Committee (HUAC) in the 1950s.

As his biographers discovered, Robbins dropped the dime on his colleagues less from fear of being blacklisted than that of being outed. A bisexual whose greatest love, many believe, was for a ballerina — Tanaquil LeClerc, the wife of his idol, George Balanchine — Robbins also had affairs with men, Montgomery Clift among them. Not only did he fear his family’s wrath, but homosexuality was then punishable by prison.

Like many artists, he’d flirted with communism and the post-World War II idea of Soviet-American friendship. All the while, the FBI was watching him. So was Ed Sullivan.

A decade before he introduced the Beatles, Sullivan was striking fear into the hearts of leftists by vetting them for his TV show, sometimes writing damning items about them in his newspaper column. In 1950, Sullivan pressed Robbins to reveal his activities and that of his fellow Soviet sympathizers, one of them Robbins’ sister. When Robbins refused, Sullivan canceled his appearance.

But three years later, subpoenaed as a “friendly witness,” Robbins caved. He gave HUAC the names of eight party members, seven of whom, Vaill said, were already known. Robbins later told “West Side Story” writer Arthur Laurents that he wouldn’t know “for years” whether he’d done the right thing.

“Oh, I can tell you now,” Laurents replied. “You were a s–t.”

Zero Mostel openly disdained Robbins. Blacklisted himself, though not through Robbins’ doing, the burly actor saw his film career wither and die. Nevertheless, he knew a genius when he saw one, and went on to star in 1964’s “Fiddler on the Roof,” which Robbins choreographed and directed.

Sheldon Harnick, the show’s lyricist, remembers that first fraught day of rehearsal, and how he and the cast awaited Robbins’ arrival. When he finally came in, Harnick said, “He and Mostel looked at each other. Then Zero said, ‘Hi, there, blabbermouth!’ and everyone broke up.”

Even so, there was always tension between the cast and their director, who never left a single moment of a show to chance — and did whatever he had to do to make his vision real.

“Maybe I’ve tried to blot it out from my memory,” Harnick, now 94, told The Post, “but Jerry could be cruel, especially to some of the women. If he had a criticism, he would express it in a particularly cold and cruel way.”

Austin Pendleton, who played the show’s timid Motel the tailor, remembers one lacerating encounter so personal, he told Robbins’ assistant not to let the director talk to him again for a week. And Robbins obeyed: “He’d say, ‘Tell Austin to cross left,’ and then, a week to the day, he was supportive again, and my performance had really pulled together.”

Now a director himself, Pendleton said, “He was harder on himself than anyone else.”

Had Robbins not been a director, he might have been a puppeteer. Or so he told Carol Lawrence, who played Maria in 1957’s “West Side Story,” when he showed her his puppet collection. It was a good metaphor for how he saw the world.

“He wanted complete control,” she told The Post. “You were under his fingertips.”

A firm believer in the method school of acting, Robbins encouraged off-stage enmity between his actors, sometimes with violent results.

Under Robbins’ direction, Larry Kert — the Tony to Lawrence’s Maria — got a nightly pummeling. “Hit him harder!” Robbins urged her as they rehearsed the scene in which Maria attacks the man who killed her brother.

One day, she recalled, Kert walked into her dressing room, his chest bandaged, and so in pain he could barely speak. “The doctor said you’re loosening my lungs from my rib cage,” he whispered. “But I can’t tell Jerry.”

Instead, Lawrence told him. “And without a second’s pause, Jerry said, ‘So hit him in the head, you won’t hurt anything there.’”

Even Bernstein, who wrote the music for that show, came in for a pounding, at least psychologically, when Robbins crossed out some of his orchestrations.

Years later, at Bernstein’s memorial service, Laurents said his “West Side Story” collaborator was afraid of only two things: “God and Jerry Robbins.”

Decades before Martin Charnin wrote and directed “Annie,” he played a Jet in “West Side Story.” He was, he told The Post proudly, the first person to sing “Gee, Officer Krupke, Krup you!” on a Broadway stage.

Now 83, he remembers watching Robbins fall into the pit. He said it happened during a rehearsal in Philadelphia.

“We wanted to see how far he would go and he ended up going one step too far,” Charnin said of himself and fellow Jets. Had the bass drum not broken his fall, Robbins would have been badly hurt. Why didn’t anyone stop him?

“I really don’t know,” Charnin said. “Maybe there was a collective moment of tit for tat . . . I’d like to believe that it was just a mistake, and we were terrified — we didn’t want him to get hurt.

“For all of how tough Jerry was, he also had something inside of him that was really good,” he continued, “and that goodness manifested itself in the work. He knew what he wanted, and what I learned and used in my career literally came from a fountain called Jerome Robbins.”

Chita Rivera, whose multi-Tony-winning career took off after her role in “West Side Story,” goes further.

“All I know is that I was in love with Jerry,” she told The Post. “I remember feeling euphoric when I saw him work — it was just so beautiful, and so right and on the nose .

“He taught us how to be. When I was running through the door to the window after [the song] ‘A Boy Like That,’ he said, ‘Don’t dance to the window. Could you just go back and walk to the window?’

“He taught us how to dance as people, not as dancers.”

It was dancers with whom Robbins chose to spend his last two decades. After “Fiddler,” he and his “West Side Story” team tried and failed to get another show off the ground. Disenchanted with Broadway, Robbins returned to where he started, making the ballets that are still being danced today.

“I think with the ballet dancers, he had a slightly gentler edge, though he could still rip and destroy someone,” said Christine Redpath, who teaches the Robbins repertoire at New York City Ballet. “He had a few people here and there he’d beat into. I remember one guy being completely devastated, in tears . . . but he survived.”

It helped that Robbins loved dogs, his own and everyone else’s. One of Redpath’s golden retrievers came in handy during the making of at least one ballet.

“When he was choreographing ‘Brandenburg’ in the early ’90s, the rehearsal pianist said, ‘I’ll give you money if you bring Emma into the room!’ ” Redpath told The Post. “So I did and she’d lie under Jerry’s seat. When he got tense, he’d look down at her and she’d look at him and he’d smile and the mood would change.”

Others noticed it, too. As “West Side Story” dancer Grover Dale told biographer Greg Lawrence a year after Robbins’ death, “I often wondered what the work would have been like had he been as sweet to his dancers as he had been to his dogs.

“Perhaps ‘contentment’ and ‘being a genius’ don’t mix very well,” Dale said.