'John Wick' director Chad Stahelski talks friendship with 'older brother' Keanu Reeves

"John Wick" director Chad Stahelski is opening up about his friendship with Keanu Reeves, who he said has been like an "older brother" to him.

The two first met when Stahelski was Reeves' stunt double on the first "Matrix" film, released in 1999. Their latest project together, "John Wick: Chapter 4," is out in theaters today.

"He was already in the action world and very, very successful," Stahelski told "Good Morning America" of Reeves' status at the time, having already starred in 1991's "Point Break" and 1994's "Speed." "I'm still kind of new even as a stuntman at that point."

"I got the job thinking it was this little sci-fi action movie -- and it was not," he added. "It's 'The Matrix.'"

Stahelski, 54, said he found an "older brother kind of vibe" with Reeves, 58, while doubling him in the "Matrix" trilogy and in 2005's "Constantine."

While Stahelski worked his way up in Hollywood, going from stuntman to stunt coordinator, he eventually came on to help Reeves with his 2013 directorial debut with "Man of Tai Chi" as the film's martial arts choreographer.

"There was a massive mentorship going on there, like learning and growing and becoming a better performer, a better stunt person, better stunt coordinator, better choreographer," Stahelski said. "But understanding it through not just what I was experiencing, but through Keanu helping mentor me and being exposed to the Wachowskis and these other great directors ... we had worked with."

Years later, when Stahelski was looking for "something off the normal beat" to direct, Reeves brought him the first "John Wick" script.

"It was a bit of an odd script. Puppy dies and this guy goes on a rampage," Stahelski recalled. "And he's like, 'Do you have a take on this? We can't quite crack it.'"

"I had this take on Greek mythology and how to blow it out and be this surreal love letter to action movies," he continued, noting that he wanted it to be "more meta than most" films and took on the idea of "don't worry about making a movie, but make a myth and make a legend."

That first film, written by Derek Kolstad and co-directed by Stahelski and David Leitch, laid the groundwork for one of Reeves' most iconic characters: John Wick, a fabled ex-hitman, nicknamed "Baba Yaga," who un-retires to seek revenge after his puppy, a final gift from his recently deceased wife, is killed.

"Keanu is game for literally anything. I mean, he's so enthusiastic and so awesome," Stahelski gushed. "So again, it's back to that mentorship of, look, we have a good sense of how to direct technically and logistically but, like, storytelling and all that stuff, we're gonna need a little help with. And Keanu was instrumental in guiding us through our 1,000 mistakes a day we'd make."

The success of the first "John Wick," made on a relatively low budget, has spawned into a full-fledged franchise that has reached epic heights with its fourth installment being one of the most-talked about movies of the year.

Stahelski said working with Reeves on the "John Wick" films has been "very much a collaborative thing" and said that their relationship is "unique because it's ever-changing."

"We laugh at our own s--- a lot of the time," he joked. "It's a very interesting relationship for sure."

As for if he and Reeves will make a fifth "John Wick" film, Stahelski said the one question they ask themselves when deciding to continue the story is pretty simple: "Why?"

Stahelski said the "why" for "Chapter 4" was to answer the question of how the legend of John Wick ends, saying "the legend has got to come to a conclusion."

"Whether the character dies or not, whether the other characters die -- irrelevant," he said. "But the character has got to come full circle ... and we had a way to do that."

"John Wick: Chapter 4" is now in theaters.