The film has more than stood the test of time, and in 2004 was inducted into the US Library of Congress’s National Film Library of “culturally significant” films. But during production, Enter the Dragon appeared snake bitten. The first-ever co-production between a Chinese film company (Golden Harvest/Concord) and a Hollywood studio (Warner Brothers), it was plagued by language barriers, script issues, and at least one physical confrontation involving its star. And the budget was significantly less than the commonly reported $850,000, claims associate producer Andre Morgan. “The whole budget was $450,000,” he tells BBC Culture. “Remember, you heard it from somebody that was there. I prepared the budget; I signed the budget.” Regardless, the profits were astronomical, with Enter the Dragon reportedly grossing $100,000,000 worldwide upon its initial release.

A star like few others

Morgan worked on the Chinese side. He was just 20 years old when principal photography commenced and celebrated his 21st birthday on the iconic hall of mirrors set that was built specifically for the climactic duel between Lee’s character and the villainous Han. He tells BBC Culture that in person Lee had a star presence unlike almost anyone else. “Bruce Lee never walked into a room in his life; he a room. When Bruce was in a room, nobody else mattered. Steve McQueen was the same,” he says. Indeed, McQueen was a close friend and student of Lee, who before hitting the big time himself, taught martial arts to a host of celebrities.

By the early 70s, McQueen, aka “The King of Cool”, had conquered Hollywood with iconic appearances in The Magnificent Seven, The Great Escape, Bullitt and The Thomas Crown Affair. Lee, who was born in San Francisco in 1940 but spent his formative years in Hong Kong, would also conquer Hollywood. After returning to the US in 1959, he made Seattle home, and attended the University of Washington to study philosophy. Soon thereafter, Lee started a family, and eventually decamped to California to pursue his film career in earnest.

But he had one major strike against him: he was Chinese. Regardless of his eye-popping martial arts skills and background as a child actor in the Hong Kong film industry, Hollywood’s biggest powerbrokers were unwilling to risk a significant investment on a 5ft-7in, 135lb Chinese leading man with a thick Cantonese accent. They were making a big mistake.

Disenchanted by his lack of progress following a decade in the US, Lee returned to Hong Kong in 1971, and became hugely successful thanks to starring roles in a trio of martial-arts actioners: The Big Boss, Fist of Fury and The Way of the Dragon, the latter of which he also wrote and directed. All cheaply made by US standards, they were record-breaking box-office smashes in Asia. That news reached Hollywood, and they came running.

Enter the Dragon was born.

How Bruce Lee changed fighting on screen

In the final analysis, the movie is a martial-arts action piece, and the fight scenes are what you’re signing up for. You don’t watch Enter the Dragon for acting, cinematography, or storyline. In fact, Michael Allin’s script was an unapologetic rip-off of the James Bond movie Dr No, complete with a hero recruited by British intelligence, mysterious island, and villain with a deadly metal hand.

But despite any shortcomings, Enter the Dragon remains the most influential martial-arts movie ever made.

As a martial artist, Lee was years ahead of his time. While respectful of traditional fighting styles such as kung fu, karate and judo, he refused to be bound by style itself. Indeed, the system that Lee founded, Jeet Kune Do (The Way of the Intercepting Fist), is a set of principles designed to work specifically for an individual. Take what is useful and make it your own. This was “mixed martial arts” long before the term became part of the combat-sports vernacular.

Acclaimed Jeet Kune Do instructor Tommy Carruthers has been studying martial arts for almost 50 years. The Scotsman teaches all over the world and has ventured to China on approximately 30 occasions. Now in his 60s, Carruthers carries the look and physique of a much younger man and remains immersed in Lee’s teachings.

In the opening scene of Enter the Dragon, which Carruthers first watched as a teenager in the mid-1970s, Lee squares off against future Hong Kong movie legend Sammo Hung. The battle sees both men sporting fingerless gloves and tight-fitting shorts, accessories which would become synonymous with the mixed martial arts-based Ultimate Fighting Championship fighters decades later.

“He wanted to be more diverse in his approach [to fighting], and educate the audience,” Carruthers says. “In that scene, you see the footwork, the feints [moves designed to distract the opponent]; there’s a knee fake before a backfist, there’s a four-punch combination akin to boxing. It’s difficult to put a label on the throwing techniques he’s using because there are a number of Japanese and Korean systems that incorporate the same moves. There’s also an element of grappling at the end of that fight.” 

But despite the education Lee was delivering, there were glaring differences between the high-kicking action that he delivered on screen, and his approach to real-life combat, as embodied in his Jeet Kune Do method. “The principles of Jeet Kune Do are economy of motion, simplicity, and being as efficient as possible,” explains Carruthers. “When you see an attacker with intentions, you shut him down – longest weapon and closest target.” There’s no time for flying through the air or backflips in a street situation: Lee’s ethos was to intercept an attack with the most damaging and direct response possible using feet or fists.

Life would imitate art on the set of Enter the Dragon. With scores of extras on the movie – many of whom were members of the Hong Kong-based triad gangs, with backgrounds in martial arts and street fighting – Lee presented a tantalising target for a real-life encounter.

If one could defeat the number one action star in Hong Kong, then fame and fortune would be theirs for the taking. On one particular day, Morgan recalls, Lee grew tired of being teased by an extra who persistently referred to the martial artist as a fraud. The issue would be settled by combat and Lee wasted no time.

“All the bullshit about the kid calling Bruce out – he could have killed that kid. He didn’t, he just humbled him,” says Morgan, who witnessed the incident first-hand. “It was over in less time than it took me to tell you what happened.”

Efficiency, however, doesn’t sell. For Enter the Dragon, Lee created some of the most sophisticated and physically demanding fight choreography ever captured on film. In addition to the hand-to-hand combat that Carruthers referenced, Lee’s use of traditional weaponry is mesmerising.

“Bruce pushed himself as hard as anyone has ever pushed themselves – to the point of exhaustion, to the point of dehydration, mental exhaustion, physical exhaustion – but it was well within his tolerance. He knew exactly what he was doing,” said Morgan.

“And then you see the magic happen. Remember, there was no video assist, so you would send the dailies to the lab every 48 hours. You couldn’t come out of [watching] those dailies without realising that you had something special. Bruce was excited. It was good stuff.”

When tragedy struck

The movie wrapped in April 1973, and expectations were high after Lee viewed a rough cut in Los Angeles. He’d flown stateside for medical tests after falling violently ill in a dubbing studio in Hong Kong. A cerebral oedema (brain swelling) almost killed him, but no one could determine its cause. Despite the terrible scare, Lee was told by doctors that he had the body of an 18-year-old, and returned to Hong Kong reassured.

However two months later, the martial-arts star lost consciousness in the apartment of Taiwanese star Betty Ting Pei. This time a cerebral oedema proved fatal. One of the most mysterious celebrity deaths of all time, the coroner ruled “death by misadventure”, reasoning that the oedema was caused by a prescription pain medication that was present at autopsy.

With Lee and Ting Pei purported to be having an affair, the Hong Kong press had a field day, and the official cause of death was roundly viewed as dubious. Controversy has loomed large over Lee’s death ever since and it remains a strongly debated topic half a century later. Other reasons that have been cited for his demise range from the ridiculous – such as him having fallen victim to the fabled martial-arts move the “delayed death touch” from an opponent, or instead a family curse – to more rational explanations such as recreational drug use, heatstroke, epilepsy and adrenal insufficiency. No one will ever know for sure.

Lee’s body was flown to Seattle for burial just days before Enter the Dragon opened at Grauman’s (now TCL) Chinese Theatre in Los Angeles. The premiere should have been a glorious occasion but was overshadowed by sadness. “There was no triumph – we’d already buried him,” said Morgan before pausing briefly. “They just sold the tickets and let everyone go in.”

Lee left behind a wife and two small children. An unfinished film of his, Game of Death, was posthumously released in 1978, but was mostly comprised of new footage with actors standing-in for Lee, and featured a only a small portion of the actual late master’s genius. In one of the scenes, Lee’s character is shot and badly wounded on a movie set before plotting revenge. In a cruel and freakish twist of fate, Lee’s son, Brandon, was accidentally shot and killed on the set of The Crow in 1993. This tragic occurrence spawned media talk of a family curse, a hypothesis which was rightly denounced.

Given what Lee achieved in just 32 years, one can only imagine what would have lain ahead of him had fate not intervened. British martial-arts movie guru Ricky Baker has been working professionally within the genre for decades and is an established authority on Bruce Lee. He believes that the late icon would have flourished.

“Warner Brothers would have allowed him to write his own ticket,” said Baker. “He had Game of Death to finish, but Bruce Lee would have widened [his horizons]. He loved acting, but he would have improved as a director and a scriptwriter. And he would have taken part in projects that were more story driven. You can’t just stay in the martial arts movie scene; you’re going to get older. He would have aimed higher and strived to be the best in different fields.  

“He would have accelerated the recognition of Asian actors and directors by the 80s. He would have used his power to bring them in and given them a testing ground. It wasn’t until Crouching Tiger, Hidden Dragon (2000) that everyone kind of jumped on it. Bruce Lee would have bridged that gap because he was already Americanised.”

An essential pioneer for a whole movie genre, widely recognised as the greatest martial artist of the 20th Century, the star of the most beloved martial-arts movie of all time. While Bruce Lee’s death was undeniably tragic, there is solace in the incredible amount of success he attained in his short life.