Keanu Reeves is used to defying death onscreen.

His action hero characters dodge bullets, bend the laws of physics, surf killer waves and stop runaway buses in classics including “Point Break” (1991), “Speed” (1994), “The Matrix” (1999) and “John Wick” (2014).

But, while the 59-year-old actor constantly escapes tragedy in movies, offscreen he has been surrounded by it.

Over the decades, he’s endured the heartbreaking loss of numerous loved ones, and his own ending, he recently revealed, is always on his mind.

“I’m thinking about death all the time,” Reeves told BBC News in an interview earlier this week to promote his new sci-fi novel, “The Book of Elsewhere.”

“There’s something ultimately about the creative gesture that comes from pain,” he added, ever the philosopher hunk.

Co-written with China Miéville, the book tells the story of a warrior who has seen hundreds of civilizations come and go but who cannot be killed, despite wishing otherwise.

It’s based on Reeves’ “BRZRKR” comic series, which features a protagonist with a square jaw, shaggy brown hair and a life filled with loss. The similarities to Reeves have not gone unnoticed, though the actor has a mythic backstory all his own.

Born in Lebanon, Beirut, Reeves moved around a lot early on. His mother, Patricia Taylor, was a British showgirl-turned-costume designer. His father, Samuel Reeves, was a Chinese-Hawaiian scientist.

Reeves’ sister, Kim, was born when he was two and the family was living in Australia. Samuel exited the picture soon after.

“The story with me and my dad’s pretty heavy,” he told Details in 1991, reluctant to elaborate further.

Various stepfathers and some time in New York followed. When Keanu was 6 or 7, Patricia settled him and Kim in Toronto. Growing up, he was at once quiet and private but social.

“It’s a particle, it’s a wave,” he told Rolling Stone of his contradictory nature in his youth, which hinted at the soulful action star to come.

He attended four different high schools, including one that he was kicked out of, before dropping out to pursue acting. He made his film debut in 1986’s “Youngblood,” as a hunky hockey player.

Soon after, he headed to Los Angeles. At 16, he signed with manager Erwin Stoff, a friend of his stepfather’s who he would go on to work with for more than 30 years.

“He is a very loyal person, he’s not a fair-weather friend,” a senior entertainment executive who has worked on several Keanu projects told The Post.

His big break came in 1989 with the iconic stoner comedy “Bill & Ted’s Excellent Adventure.”

Around the time the film was being made, he nearly died in a motorcycle accident on Los Angeles’ twisting Topanga Canyon Boulevard.

He hit a hairpin turn going too fast and laid on the road for a half hour before helped arrived. At one point, a truck sped past and ran over the helmet he’d been wearing and had removed as he lay there.

“I remember saying in my head, ‘I’m going to die,’” he told Rolling Stone. “I call that a demon ride.”

Ultimately, his spleen had to be removed and he was left with a thick scar on his stomach.

But, such incidents didn’t tame him. The1991 Details interview portrayed him as defiantly riding without a helmet, calling California’s law requiring such head protection “petty government bulls—t.”

(In recent years, the entertainment executive told The Post of Reeves riding up to meetings on motorcycle, thankfully wearing a helmet, which he’d remove cinematically and set on the boardroom table.)

With such a penchant for danger, it was natural that Reeves eventually formed a tight bond with the reigning bad boy of the era, River Phoenix.

The two were introduced by Martha Plimpton, who was dating Phoenix and had co-starred with Reeves in the 1989 comedy “Parenthood.”

The young stars quickly grew close, thanks to a shared love of music and aversion to Hollywood’s glitz. They also had unstable, traumatic childhoods in common; Phoenix had grown up in the Children of God cult and reported being sexually abused as a 4-year-old.

The two went on to appear together in “I Love You to Death” (1990) and, more notably, “My Own Private Idaho” (1991), as two gay hustlers on the streets of Portland, Oregon.

“They were really talented, and they were also sort of profoundly beautiful,” the latter film’s director, Gus Van Sant, recalled.

The shoot was a memorable one, from the various sex scenes to Phoenix and Reeves and much of the young, testosterone-heavy cast — which also included Flea from the Red Hot Chili Peppers — taking over Van Sant’s house. They slept on futons scattered about, had late-night jam sessions in the garage and held so many raucous parties the director ultimately moved out for a spell.

But the good times soon came to a tragic halt.

On Halloween night in 1993, Phoenix collapsed from a drug overdose outside of the famed Viper Room club in Hollywood and died.

Reeves, who was in production on “Speed” at the time, has seldom spoken about losing his dear friend.

“I hate speaking about him in the past,” he has said. “He was a really special person, so original, unique, smart, talented, fiercely creative.”

Meanwhile, Reeves’ sister Kim spent most of the ’90s battling leukemia. Although he was one of the most in-demand movie stars in the world at the time, her brother was right by her side.

“Keanu helped me so much through my illness,” Kim told Australia’s Woman’s Day. “When the pain got really bad, he would sit with me and hold my hand, and keep the ‘bad man’ from making me dance. He was supporting me and comforting me all the time, even when he was away.”

Reeves also reportedly donated tens of millions of dollars to cancer research.

But, while he is and was close to his sister and mother, he cut his father squarely out of life.

In 1994, Samuel Reeves was arrested for possessing large quantities of cocaine and heroin and sentenced to 10 years in jail. He served two years, and, at some point in the mid-90s, reached out to his son but Keanu didn’t get back to him.

Samuel died in 2018, and Reeves reportedly did not attend the funeral and memorial luncheon, held at the famed Duke’s Waikiki on Oahu.

“It’s full of pain and woe and f—ing loss and all that s–t,” he once said of their relationship.

The year 1999 saw Reeves’ biggest hit — “The Matrix” — but also his biggest loss.

His girlfriend Jennifer Syme was eight months pregnant when she gave birth to their baby daughter, Ava. She was stillborn.

Syme and Reeves had only been dating a year or so but were reportedly deeply in love. But, their relationship could not withstand the tragedy. They broke up a few weeks later but remained close.

In 2001, Syme hit several parked cars after partying at Marilyn Manson’s house. She was thrown from her Jeep Cherokee and suffered deadly head injuries. She was just 28-years-old.

Reeves said little about her death at the time. Five years later, in a revealing interview with Parade magazine, he admitted he was never the same after her passing.

“Grief changes shape, but it never ends,” he said. “People have a misconception that you can deal with it and say, ‘It’s gone, and I’m better.’ They’re wrong.”

He was 41 at the time he gave the interview, and said he still hoped to have a family of his own someday.

“I want to get married. I want to have kids. That’s at the top of the mountain. I’ve got to climb the mountain first,” he said. “I’ll do it. Just give me some time.”

Yet, those desires seemed to allude him. Reeves has never had children of his own, at least that the public is aware of.

For a handsome, successful movie star, his romantic life has often been a mystery.

“You don’t hear about him boffing starlets,” said the entertainment executive.

What you do hear about is him being a nice guy — known for being exceedingly loyal, charitable and down-to-earth.

“He not a diva,” said the executive. “He’s very pragmatic, he’s seen it all and done it all. He’s got savvy but not annoying savvy — unlike Ryan Reynolds and all his businesses.”

In 2010, the mystery around Reeves, his past losses and a photo of him looking alone and forlorn on a park bench came together as the “Sad Keanu” meme.

“I’m just eating a sandwich,” he later said of the photo, denying it had captured him at any kind of low moment.

Indeed, Reeves isn’t alone these days.

In 2019, he made his red carpet debut with longtime friend-turned-girlfriend Alexandra Grant.

Grant, a willowy, silver-maned artist, just six years younger than Reeves, is a refreshingly interesting, age-appropriate love interest for a Hollywood leading man — a notable change from the girls contemporaries such as Brad Pitt, 60; Tom Cruise, 62; and Leonardo DiCaprio, 49, are seen out with.

And, he’s channeled his energy into the John Wick movies.

That four-film franchise has been an unexpected hit, raking in more than $1 billion at the box office, with each successive movie more successful than the last.

While he didn’t have a producing credit on the early John Wick films, Reeves was heavily involved in shaping them to be successful.

“He was at most every test screening, at every meeting with the studio,” said an insider.

The titular character — a hit man who reluctantly comes out of retirement to avenge the death of his dog — seems to really resonate with the brooding star.

“I love his grief,” he told The Guardian of the character.