Leonardo DiCaprio at the 2016 Golden Globes, left, and in "This Boy's Life" in 1993. (Mario Anzuoni/Reuters; Warner Bros./Courtesy Everett Collection)

Editor’s note: Leonardo DiCaprio won his first Academy Award for his lead role in “The Revenant” on Feb. 28, his sixth career nomination.

Leonardo DiCaprio as an adult is a heartthrob, a smooth talker, a romancer of supermodels. Leonardo DiCaprio as a teenager was so nervous around girls that he turned to his “Growing Pains” co-star Alan Thicke for flirting advice.

“He said, ‘How do I get her number?’ ” Thicke recalls two decades later, remembering when 17-year-old DiCaprio had a crush on a cute extra. The veteran actor told DiCaprio to look in the wardrobe department, where everyone’s contact information was posted on a wall. “I’m sure he feels he owes most of his adult social life to that tip.”

While DiCaprio is well-known for that infamous social life (the models, the yachts, the boozy weekends in Ibiza with Orlando Bloom and Justin Bieber), he’s also cultivated a persona as one of his generation’s most serious actors. This year, award season chatter has focused on his grueling preparation for his lead role as a vengeful frontiersman in the “The Revenant,” which will likely — finally — result in his first-ever win at the Academy Awards on Sunday night.

But many years before DiCaprio, 41, risked hypothermia and ate raw bison liver while shooting “The Revenant,” he was the unknown child actor who ran for cover on the set of “The New Lassie” when an episode featured a rattlesnake, according to the director, Renny Temple. Then he was just Leo, the precocious teen who started in commercials for Bubble Yum and Kraft fat-free cheese singles, and landed his first movie role in 1993’s “This Boy’s Life” after Robert De Niro saw the auditions and said, “I like the blond kid. He’s quite good.”

Eventually “Titanic” came along in 1997 and hordes of teen girls made repeated trips to the multiplex to gaze into Leo’s piercing blue eyes and sob when Kate Winslet said “I’ll never let go, Jack!” But those who knew him before “Titanic” say he worked hard to retain his grasp on normalcy while on the cusp of fame. It wasn’t always easy.

“He wasn’t quite the same as being normal — it was impersonating normal,” said New York Magazine theater critic Jesse Green, who profiled DiCaprio for the New York Times Magazine in 1995 as the young actor was filming “The Basketball Diaries.”

The story describes DiCaprio, a newly recognizable name after landing an Oscar nomination for “What’s Eating Gilbert Grape,” as being a bit odd and kind of a dork: Doing impressions and playing around with the P.A. system in his $35,000 Jeep Grand Cherokee, the only hint of his new wealth. “Maybe it was a bit of a defense mechanism . . . he took great pains to not seem like a Hollywood a--hole,” Green said. “It was better to seem like a teenage idiot.”

‘Up to no good’

The cast of “Growing Pains,” from left, Jeremy Miller, Tracey Gold, Kirk Cameron, Ashley Johnson, Joanna Kerns, Alan Thicke and Leonardo DiCaprio in 1991. (Courtesy Everett Collection)

If DiCaprio was rattled by the sudden taste of fame, he tried not to show it. After all, he worked hard to get into the spotlight. Growing up in Los Angeles, he convinced his parents in elementary school that he wanted to be an actor. He appeared in commercials and on shows like “Mickey’s Safety Club,” and after stints on the “Lassie” TV revival and NBC’s first attempt at a “Parenthood” show around age 15, he wound up on ABC’s “Growing Pains” in 1991.

Producers cast DiCaprio as a homeless teen taken in by Kirk Cameron’s character’s family. Joanna Kerns, who played Cameron’s mother, remembers DiCaprio as especially intelligent and disarming for his age. Still, he was no angel: He loved to mess around on set and make fun of his co-stars.

“He was totally mischievous,” Kerns said. DiCaprio’s good friend, actor Tobey Maguire, used to come by the set: “They looked like they were really up to no good.”

While casting agents and directors recognized his raw acting ability, DiCaprio had to grow up. In 1992, DiCaprio — who was unavailable for comment for this story — was chosen out of 400 young men for the role of De Niro’s abused stepson in “This Boy’s Life,” his first major film role. (He would prefer that you forget about “Critters 3.”)

Michael Caton-Jones, the director of “This Boy’s Life,” recalls DiCaprio needed some serious coaching, as he was going through his most impressionable teenage years while they were filming.

Leonardo DiCaprio and Robert De Niro in 1993’s “This Boy’s Life.” (Warner Bros./Courtesy Everett Collection)

“He came with a bunch of habits that we got rid of,” Caton-Jones said. Namely, DiCaprio had no idea how to behave on a movie set. DiCaprio remembers this, too: He recently told Deadline that “if I was telling too many jokes, or cracking up, or trying to converse with the crew members,” Caton-Jones would be quick to chastise him.

“I felt there were two things that could happen: I felt he could buckle down and become fantastic, or he could become an a--hole and his career would be shot,” Caton-Jones said. He’s especially proud that during filming, he adopted a “tough love” mentoring style, teaching DiCaprio Hollywood lessons.

“How to work with a director, do your homework, educate yourself,” Caton-Jones ticked off. “You’ll get famous, if that’s what you want — but not if you don’t do the work.”

After filming wrapped, Caton-Jones was pleased by DiCaprio’s evolution; he had come to think of him as a little brother. Years later, DiCaprio would get in touch “when the whole movie star stuff was freaking him out a bit” and Caton-Jones kept reminding him: Just do the work.

And when Swedish director Lasse Hallström called to ask about casting DiCaprio as Johnny Depp’s mentally disabled brother in his new drama “What’s Eating Gilbert Grape,” Caton-Jones had simple advice: “If you can get the kid, get the kid.”

‘Leo has this innocence’

At first, Hallström wasn’t totally sold, thinking DiCaprio (drowning in fan mail from girls who loved him as the dreamy boy on “Growing Pains”) was too classically good-looking for the role. Then DiCaprio nailed the audition. Of all the actors who tried out, “Leonardo was the only one who had picked up on the essentials, the body mannerisms, and integrated them. He was the most observant,” Hallström said to the New York Times.

DiCaprio took preparation very seriously, impressing even Depp, who recently admitted at the Santa Barbara International Film Festival that he “tortured” DiCaprio during the film. (“No, I will not give you a drag of my cigarette while you hide from your mother again, Leo.”) When the movie debuted, critics were blown away by 18-year-old DiCaprio’s performance, which earned him a supporting-actor Oscar nomination.

DiCaprio was intent on playing the long game.“Being the hunk of the month annoys me — they bring you in like a piece of meat, saying, ‘Here’s the next cute kid’ — and it could ruin your career,” he told the L.A. Times. “I’m looking for longevity.”

There were some missteps, such as the flop “The Quick and the Dead,” a low-grossing drama with Sharon Stone — who, as the story goes, was so insistent on having DiCaprio in the film that she offered to personally pay his salary.

Soon, other casting directors sought him out. “The Basketball Diaries,” in which he played a drug-addicted athlete, united him with Mark Wahlberg.

“Leo had this innocence . . . that would draw you in to care about him so much,” said casting director Avy Kaufman, who took DiCaprio and Wahlberg to dinner to help them bond. “He was a just a nice kid.”

Romeo on-screen, and Falstaff off

As prepared as DiCaprio was at work, rumors about his personal life blew up when he arrived in New York to film “The Basketball Diaries” in 1994. The tabloids loved to write about his hard-partying posse, made up of dudes from Maguire to Kevin Connolly to David Blaine.

“He seldom sleeps, so intense is his partying,” gossip columnist Liz Smith wrote. His love life became fodder: Was he dating Juliette Lewis? Bridget Hall? Alicia Silverstone? Rolling Stone reported him “brawling” at Manhattan nightclubs.

Green, who wrote the New York Times profile, said DiCaprio claimed that it was all exaggerated — and really did appear fairly grounded.

“They make it sound like I go to clubs to wreck myself silly, get into fights, sleep with all the ratty girls there. It’s true that while we were filming, Marky and I went out for a little dancing, a little socializing, a little flirting,” DiCaprio told Green. “And one morning we wake up to find that, according to the paper, I picked a fight with Derrick Coleman, forward for the New Jersey Nets! Like I’m going to get into an argument with him . . . he’s six foot a hundred.”

“People want you to be a crazy, out-of-control teen brat,” DiCaprio continued. “They want you miserable, just like them. They don’t want heroes; what they want is to see you fall.”

While headlines about DiCaprio’s social life would only increase, the mid-1990s simultaneously brought him new professional credibility with“Romeo + Juliet.” Director Baz Luhrmann always wanted DiCaprio to be Romeo, casting director David Rubin said — the hard part was finding the leading lady. His chemistry with Claire Danes sealed the deal. Natalie Portman auditioned, but the studio nixed it because of their age difference. (“Fox said it looked like Leonardo DiCaprio was molesting me when we kissed,” Portman later explained.)

Leonardo DiCaprio in “The Revenant,” searching for revenge — and an Oscar. (Twentieth Century Fox/Courtesy Twentieth Century Fox)

That led to a little movie called “Titanic,” which of course made him an international superstar. Though the tabloids were having a ball writing about DiCaprio’s off-screen debauchery, he maintained the respect of people in the industry.

“[Leo was] totally grounded,” said Jerry Zaks, who directed DiCaprio in the 1996 drama “Marvin’s Room,” his final pre-“Titanic” movie. “It was like, no airs, no bull----, no attitude, no diva crap. And believe me, it’s not always like that.”

Almost 20 years later, with four more Academy Awards acting nominations under his belt, some of DiCaprio’s former co-workers aren’t surprised to see his success.

Alan Thicke — who lately only sees DiCaprio if they both attend a “rager” thrown by his son, “Blurred Lines” singer Robin Thicke — counts himself as one of DiCapio’s biggest fans.

“Frankly, there are some young turds in the business,” Thicke said. “You kind of know who you want to root for. Leo is one of those guys everyone rooted for . . . just about anyone would tell you they enjoy celebrating by proxy.”