In the spring of 1963, already popular from his big-screen breakout as one of The Magnificent Seven and just a couple months away from entering the Badass Hall of Fame with the release of The Great Escape, Steve McQueen was on the brink of superstardom.
Intrigued by his dramatic backstory and his off-screen exploits — McQueen was a reformed delinquent who got his thrills racing cars and motorcycles — LIFE sent photographer John Dominis to California to hang out with the 33-year-old actor and, in effect, see what he could get.
[Below: In a video exclusive, McQueen’s ex-wife, Neile Adams, shares her memories of the ups and downs of their intense 16-year marriage.]
Three weeks and more than 40 rolls of film later, Dominis had captured some astonishing images — photos impossible to imagine in today's utterly restricted-access celebrity universe. Here, LIFE.com presents a series of pictures — most of which never ran in LIFE — from what Dominis would look back on as one of his favorite assignments, along with insights about the time he spent with the man who would soon don the mantle, "the King of Cool."
Trailing Steve McQueen was Dominis' first Hollywood gig. "I liked the movies, but I didn't know who the stars were; I was not a movie buff," Dominis told LIFE.com. But he got the assignment because he and McQueen shared one vital passion: car racing.
"When I was living in Hong Kong I had a sports car and I raced it," Dominis says. "And I knew that Steve McQueen had a racing car. I rented one, anticipating that we might do something with them. He was in a motorcycle race out in the desert, so I went out there in my car and met him, and I ask him, 'You wanna try my car?'"
Later the two of them would zip around Los Angeles together. "We went pretty fast — as fast as you can safely go without getting arrested — and we'd ride and then stop and trade cars. He liked that, and I knew he liked it. I guess that was the first thing that softened him."
From early morning until late at night, Dominis followed McQueen through his action-packed days: camping with his buddies, racing his various vehicles, playing with his family, tooling around Hollywood. Even back then, Dominis says, he had to be mindful that his constant presence did not become irritating.
"Movie stars, they weren't used to giving up a lot of time," he says. "But I sort of relaxed in the beginning and didn't bother them every time they turned around, and they began to get used to me being there.
In 1963 McQueen had been married to Neile Adams for seven years (they had two young children) but the spark between them was still very much alive. "They were always necking!" says Dominis, who also remarked upon their childlike way with each other in notes he filed for LIFE's editors back in '63: "They chase each other around," he wrote, "as though it were going out of style."
"With strangers, I can't breathe," McQueen told LIFE. "But I dig my old lady."
"I was very surprised" when Steve and Neile divorced in 1972, Dominis says. "But I lived in New York, and I never saw them [after the shoot was over]. We weren't real friends, but we were friendly. They liked me, and they had a silver mug made: 'To John Dominis, for work beyond the call of duty.' I've still got it today."
At the beginning of the LIFE shoot, McQueen participated in a 500-mile, two-day dirt bike race across the Mojave Desert.
"These people are not the wild motorcycle bums who go roaring through town a la Brando [in The Wild One]," wrote Dominis in his notes. "Rather they comprise doctors, lawyers, businessmen, mechanics, and others who enjoy the competition and the open country."
Not only was he one of the few competitors to complete the race, LIFE reported, but he also led his amateur class for most of the way, until his bike broke down three miles from the finish.
"He liked camping, he liked rugged things, he liked firing a gun," says Dominis. ("I'd rather wake up in the middle of nowhere than in any city on earth," he told LIFE.)
He also very much liked his cigarettes: Like many Hollywood stars of the time, McQueen was an unapologetically heavy smoker, and did not break the habit until he became sick in the late '70s.
Seventeen years after Dominis made these photos, the actor was dead at just 50 years old, suffering a heart attack following a risky operation to remove the cancerous tumors laying waste to his body. Though Dominis never saw or spoke with McQueen after 1963, he continued to follow his movies, and cherished those three weeks they got to know each other.
"He was very open and playful," says Dominis, "and just doing the things that he loved to do."
Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter at @LizabethRonk.