When a snapshot of Elon Musk and Ghislaine Maxwell surfaced on social media in 2020, the Tesla and SpaceX chief executive took to Twitter — as he so often does — to explain why he had been photographed with the British socialite, who was later convicted of sex trafficking in connection with the financier Jeffrey Epstein.

“Don’t know Ghislaine at all,” Mr. Musk tweeted in July 2020. “She photo-bombed me once at a Vanity Fair party several years ago. Real question is why VF invited her in the first place.”

It’s not surprising that Mr. Musk felt he had to answer for the photograph, which had been taken six years earlier at the magazine’s Oscars party. His personal life is frequently the subject of intense speculation.

As it turns out, their meeting was slightly more than a photo bomb.

According to a Vanity Fair staff member at the time who stood next to Ms. Maxwell and Mr. Musk and shared contemporaneous notes with The Times, the pair chatted. Ms. Maxwell asked Mr. Musk if there were a way to remove oneself from the internet and encouraged Mr. Musk to destroy the internet; Mr. Musk demurred. Ms. Maxwell then asked Mr. Musk why aliens hadn’t yet made contact with humanity, to which Mr. Musk replied that all civilizations eventually end — including Maxwell’s hypothetical alien one — and raised the possibility that humans are living in a simulation.

Such encounters are not unusual for Mr. Musk. He’s the world’s richest man and the tech world’s equivalent of a rock star, which brings him into contact with a motley parade of people at glittering gatherings all over the world, with occasionally awkward results.

Mr. Musk had a difficult childhood, in which he was bullied and attacked (to the point of hospitalization) by classmates. Now, at 51, he seems to be living the teenage years he never had — parties, drugs, popular friends, beautiful girlfriends, jokes cracked to an adoring audience — without quite escaping his own innate insecurity.

Mr. Musk’s image is inextricably tied to the eye-popping valuation of his companies. His professional life is remarkably dramatic — see: the ongoing soap opera of whether he will in fact buy Twitter — but of late, his personal life is even more so.

This summer alone, Insider reported that SpaceX had made a $250,000 payment to a flight attendant in exchange for what she said was her silence over sexual misconduct by Mr. Musk. The Wall Street Journal reported that an affair between Mr. Musk and Nicole Shanahan, the wife of a Google co-founder, Sergey Brin, had ended both the couple’s marriage and the two men’s friendship. And Mr. Musk confirmed to Page Six that he had welcomed twins with one of his executives — weeks before welcoming a second child with his on-again, off-again girlfriend, the singer Grimes.

To better understand Mr. Musk’s life, The Times interviewed more than 40 people who have spent time socially with Mr. Musk over the past 15 years. Many spoke on the condition of anonymity for fear of personal or professional repercussions; because of the Twitter lawsuit, for which several of Mr. Musk’s friends have been subpoenaed; or because they had attended events with Mr. Musk that required them to sign legally binding nondisclosure agreements to enter.

They describe someone whose closest friendships (many of them longstanding) are with other wealthy tech luminaries of middle age. He regularly takes meetings until 9 or 10 p.m., but when he goes out, he does so with frenetic bombast, almost as if live-action role-playing a billionaire playboy. A fan of lavish costume parties, Mr. Musk revels in settings, like the desert art festival/rave Burning Man, where he can take on a role outside himself.

At more conventional events, Mr. Musk tends to arrive late and often slips in a back entrance. Frequently approached in such settings by strangers, Mr. Musk favors intense, one-on-one conversations — one person described a party conversation with him for 90 unbroken minutes about astrophysics.

Mr. Musk did not respond to multiple requests for comment.

Work Friends Who Are Party Friends

Mr. Musk once acknowledged in an interview with Axel Springer’s chief executive, Mathias Döpfner, that he gets lonely; in a 2017 interview with Rolling Stone, he said that as a child he vowed to never be alone.

One obvious way that he staves off loneliness is using Twitter. Mr. Musk, who frequently responds to the many Regular Joe accounts that tweet at him, uses the service almost every day, in a way that suggests the website is an outlet not just for his ideas but for his emotions.

He has tweeted about his love for his children, a romantic line from a Robert Frost poem, advice about the nature of happiness and recommendations for better sleep. He has described his own Twitter habit, in conversation, as a kind of delayed adolescence.

Mr. Musk claims he hardly ever takes vacations. According to Sam Teller, a venture capitalist who was Mr. Musk’s chief of staff from 2014 to 2019, the billionaire celebrated his 48th birthday in a small conference room at the Tesla factory in Fremont, Calif., with a cake and a half dozen co-workers.

“I spent almost every day with Elon for five years — apart from family time, he spends nearly every waking hour working,” Mr. Teller said. “If your idea of fun is a long weekend of rocket engineering in a humid, sparsely populated corner of South Texas, then you should be jealous of Elon’s social life.”

Mr. Musk compresses his calendar into gaps in his hectic working schedule: a night in Cabo here, a weekend in Spain there, with jet lag exacerbating his well-known sleeping problems.

And the line between Mr. Musk’s work life and his personal life is blurry.

Many of his closest friends are longtime investors in his companies and share his technical worldview and his geeky preoccupations. Mostly in their 40s and 50s, these friends often see Mr. Musk at quiet dinners in the private back rooms of restaurants — low-key affairs in which the conversation turns to subjects like science fiction or World War II fighter planes.

His group of confidants includes Luke Nosek, who worked with Mr. Musk at PayPal and would go on to start the high–profile venture capital firm Founders Fund with Peter Thiel, and Antonio Gracias, a private equity investor who served on Tesla’s board for 14 years. (Mr. Musk gave him the second-ever Tesla Roadster.)

Mr. Musk still seems to be seeking the approval of at least one of his former colleagues.

In late August, Mr. Thiel hosted a party at his Bel Air home to celebrate the 20th anniversary of PayPal’s initial public offering.

Rebecca Eisenberg, a lawyer in Palo Alto, Calif., who was senior counsel at PayPal from 2001 to 2007, was catching up with Mr. Thiel, she said, when Mr. Musk broke into the conversation. According to Ms. Eisenberg, Mr. Musk expressed his opinion that China was likely to invade Taiwan and that the American workers at a new Taiwan-owned chip factory in Arizona would never be as skillful as their Taiwan counterparts. Mr. Thiel, meanwhile, was largely quiet.

“I have two teenagers and four pets,” Ms. Eisenberg said. “It seemed like Peter was the dominant dog, and Elon was trying to impress him.”

Mr. Musk frequently receives business advice — sometimes solicited, often not — from his friends. This, in turn, dragged some of his inner circle into his legal proceedings with Twitter, including David Sacks, whose investments at his firm, Craft Ventures, include Uber, Slack, Quora, and Airbnb, the investor Jason Calacanis and the venture capitalists Steve Jurvetson and Joe Lonsdale. In text messages later made public as a result of Twitter’s lawsuit against him, Mr. Musk admonished Mr. Calacanis for soliciting investment from “randos” for the Twitter deal: “It makes it seem like I’m desperate.”

(All of these men declined to comment for the article.)

This crowd of nerds turned moguls is also known for opulent celebrations. They hire celebrity musical guests — Cardi B, David Lee Roth — and rent out entire resorts or even historical sites. Mr. Musk’s friend Ken Howery, a PayPal co-founder who served as President Donald J. Trump’s ambassador to Sweden, threw himself a birthday party at an imposing 19th-century castle outside Stockholm in November 2020. (On Twitter, Mr. Musk said that he had gotten the coronavirus on that trip from “a visiting American.”)

Mr. Jurvetson hosted a June 2017 party at his Bay Area home that became a small scandal after Vanity Fair characterized it as a “sex party.” (Mr. Musk, who was there, disputed this, calling the party in a statement to Wired Magazine “boring and corporate, with zero sex or nudity anywhere.”) A guest at another party hosted by Mr. Jurvetson — this one with Moby as D.J. — told The Times of having seen Mr. Musk participate in a “cuddle puddle,” a form of typically nonsexual group snuggling that is popular in the Bay Area.

Mr. Musk, too, has thrown a series of lavish birthday celebrations, including one in a castle in England and one aboard the Orient Express, a luxury train. He has also hosted theme parties that at least once included live jousting on horseback. At a Japanese-themed party he threw in Tarrytown, N.Y., Mr. Musk injured his back while grappling with the sumo wrestling world champion.

Sometimes these celebrations last an entire weekend, as did a recent 40th birthday party for Mr. Jurvetson’s wife at the couple’s estate in Half Moon Bay, Calif. The public got a glimpse of the party when Mr. Musk sent The New York Post a selfie with Mr. Brin in the background, as a counter to The Journal’s report that Mr. Musk’s reported affair with Mr. Brin’s wife had ended the men’s friendship.

(Mr. Brin did not respond to several requests for comment.)

Playing a Part in Hollywood

Born in 1971 in South Africa, Mr. Musk moved to Canada for college before transferring to the University of Pennsylvania, graduating in 1995. In college, Mr. Musk and Adeo Ressi, a longtime friend who is now chief executive of VC Lab, which trains aspiring venture capitalists, ran a makeshift nightclub out of their house. Mr. Ressi has described occasionally stepping out of the parties to find Mr. Musk upstairs playing a video game alone. (Mr. Musk made reference to having Asperger’s syndrome when he hosted “Saturday Night Live” in 2021.)

Mr. Musk made his first fortune in 1999 when he sold his company, Zip2, a software start-up that created online city guides, to Compaq for $22 million. The same year, he started X.com, a payments company that would eventually turn into PayPal.

In 2002, the sale of PayPal vaulted Mr. Musk’s worth past $100 million; the same year, he founded SpaceX in the Los Angeles suburbs. There, Hollywood — and its nightlife — found him. They wanted Mr. Musk to play a part, that of the Silicon Valley prodigy trying to save the world.

“He was a curiosity and a bauble when he first moved, because there were no tech kingpins in L.A.,” said Ashlee Vance, the author of the 2017 biography “Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future.”

Ari Emanuel, the WME power agent, cold-called Mr. Musk. Leonardo DiCaprio begged him for a Tesla Roadster. With his first wife, the Canadian novelist Justine Musk, Mr. Musk moved into a house in Bel Air between the music mogul Quincy Jones and Joe Francis, creator of the “Girls Gone Wild” adult video franchise.

In an essay for Marie Claire, Ms. Musk recalled partying in Hollywood in the mid 2000s with Mr. DiCaprio and Paris Hilton and lounging on Richard Branson’s private island with Bono.

Mr. Musk invested in a Los Angeles nightclub, Deep, which The Los Angeles Times described in 2001 as “about excess and hedonism, truly titillating, madly decadent” and “deeply voyeuristic.”

“There was something incredibly boyish and charming about him,” said Vanity Fair’s former editor Graydon Carter, who hosted the billionaire at the magazine’s Oscar parties. “He was better looking than all the other tech guys.”

In person, Mr. Musk was low-key. In 2008, Mr. Carter hosted a dinner at his Greenwich Village restaurant, the Waverly Inn, to which Mr. Musk brought his mother, the model Maye Musk — who charmed the room, as her son sat mostly quiet.

By the early 2010s, after Robert Downey Jr. had used Mr. Musk as inspiration for the Tony Stark character in “Iron Man,” Mr. Musk was a major celebrity in his own right, easily the biggest star to emerge from the tech world since Steve Jobs.

“This success and a lot of money have made him even more like a big kid in the world’s greatest candy store,” Mr. Carter said.

Mr. Musk has been married twice. After divorcing from Ms. Musk, who is his age, in 2008, Mr. Musk married the actress Talulah Riley, 14 years his junior. Following his split with Ms. Riley, Mr. Musk dated the actress Amber Heard, who is 15 years younger than he, before in 2018 partnering with the singer and producer Grimes, who is 17 years younger. Mr. Musk has nine children: five with Ms. Musk, two with Grimes and two with Shivon Zilis, who is an executive director of operations and special projects at Neuralink, one of Mr. Musk’s companies. (Mr. Musk has publicly asserted that low birthrates are a threat to civilization.)

Elon for You

In 2020, Mr. Musk moved from California to Texas, but he has kept close connections in Hollywood. He has remained a member of the ultraexclusive San Vicente Bungalows, a club in West Hollywood that requires guests to place opaque stickers over the cameras on their phones. Though the lushly appointed club has a dining room, a bar, a pool house and a screening room, Mr. Musk is frequently seen there in an area called the smoking garden, where guests go to mingle with new people and flirt.

When he stays in Los Angeles, Mr. Musk frequently crashes at the Beverly Hills home of the “super-networker” and Hillary Clinton bundler Michael Kives — an influential agent turned venture capitalist who has invested in several of Mr. Musk’s companies. Mr. Kives, who used to represent A-listers such as Arnold Schwarzenegger and Bruce Willis, has been friends with Mr. Musk for years.

Recently, Mr. Musk dined at Mr. Kives’s home with Bill Maher, the HBO host; Brian Grazer, the Hollywood superproducer; and Bobby Kotick, the chief executive of the gaming giant Activision Blizzard, which publishes Call of Duty. Lloyd Blankfein, the former Goldman Sachs C.E.O., called in via video chat.

Mr. Musk has maintained a decade-long friendship with Kanye West; this week, Mr. Musk tweeted that he had talked to Mr. West about recent antisemitic comments by the musician, which he hoped Mr. West “took to heart.”

And this May, Mr. Musk attended Mr. Emanuel’s star-studded St. Tropez wedding, alongside a crowd that included Diddy, Larry David and Emily Ratajkowski; according to people at the wedding, Mr. Musk was seen in a lively conversation with Mr. David.

Mr. Musk’s friendship with Mr. Emanuel would later provide one of the year’s most memorable tabloid photographs, of the WME boss hosing off the barrel-chested tech executive aboard a yacht off the coast of Mykonos. (In recent weeks, according to a Bloomberg report, Mr. Emanuel worked to broker a peace between Mr. Musk and Twitter.)

Mr. Musk, in his style, tweeted through it. Responding to a meme comparing his body to a French bulldog’s, he wrote, “my calves are bigger tho.”

Despite all the public hobnobbing with glittery celebrities, Mr. Musk seems to identify more with another, considerably less glamorous stratum of Hollywood: comedy writers, a tribe of people who have often spun their social discomfort into humor.

The billionaire, who is known to halt meetings in order to watch “Monty Python” clips, has made a habit of socially cultivating buzzy comedians and comic entertainers. One such comedy writer said he believed that Mr. Musk had a deep-seated need to be recognized as funny.

Mr. Musk has, in particular, pursued a friendship with one comedian whose public image revolves around the outrageous steps he takes to relate to other people: Nathan Fielder, who first became famous for his Comedy Central show “Nathan For You,” which turned a series of preposterous business ideas, including excrement-flavored frozen yogurt and athletic apparel dedicated to raising Holocaust awareness, into the definitive parody of modern American entrepreneurship.

Mr. Musk — a huge fan — invited Mr. Fielder to lunch at SpaceX in 2016.

For years afterward, the famous businessman invited the famous fake businessman to his parties and would strain to make the deadpan Canadian laugh.

Mr. Musk set up a similar meet-and-greet with Dan Harmon and Justin Roiland, the creators of the animated comedy series “Rick and Morty”; he voiced an alternate version of himself, named Elon Tusk, in the show’s fourth season.

At the Edge of a Burning Man Party Scene

Mr. Musk is close with his younger brother Kimbal, who used the money he made in business with Elon to start his second career in philanthropic food sustainability (and now, the blockchain).

The more outgoing Kimbal, who favors a cowboy hat, shares with his wealthier older brother a passion for Burning Man, the annual art festival/psychedelic rave in the Nevada desert.

Mr. Musk has gone almost every year for the last two decades, often driving around in a lavishly decorated car built from the chassis of a Tesla. This year — also wearing a cowboy hat and a duster coat — Mr. Musk was seen striding arm in arm with friends through the festival, despite the pending lawsuit over the Twitter purchase. (While at Burning Man, Mr. Musk took a rare break from Twitter.) Security guards trailed behind him, conspicuous in their plain dress.

Kimbal Musk provides his brother entree to a related global social circuit. Throughout the year, at resorts and private homes in Ibiza, Mykonos, Miami, San Francisco and elsewhere, moneyed Burners convene for small festivals, guided meditations and plain old parties. Kimbal is central to this scene, and while Elon is at its periphery, his potential attendance at parties is a reliable source of excitement.

Kimbal’s close friend Bear Kittay, who formerly had the official title of social alchemist and global ambassador of Burning Man, throws what one attendee referred to as “sexy parties” that often last an entire weekend at Hotel el Ganzo in Los Cabos, Mexico, at which Mr. Kittay is a partner and where Mr. Musk has vacationed. (Mr. Kittay did not respond to requests for comment.) In this milieu and at these parties, according to several attendees, partner sharing is common.

Among the attendees’ favorite topic of conversation is the shape of the world to come. Their drugs of choice are MDMA and psilocybin mushrooms.

In recent years, Mr. Musk’s middle-aged experimentation has become public knowledge. In 2018, Mr. Musk smoked a joint on Joe Rogan’s show. That same, year, Tesla board members told The Times they worried about the way Mr. Musk’s use of Ambien had affected his tweeting, and some were aware that he had “on occasion” used recreational drugs. Mr. Musk likes to share a chart explaining that MDMA and mushrooms are better for human health than alcohol, according to one person he showed it to on a laptop while on vacation.

“I have been with him on mild exploratory journeys,” said David Marglin, a Bay Area lawyer who met Mr. Musk at Burning Man and has been his friend for 20 years. “And he appreciates the value of those journeys. Nothing out of control or wild, but it’s all night, and there’s dancing and revelry.”

Mr. Musk has tried to bring some of the Burning Man spirit into his business life, with sometimes puzzling results.

In July, The Journal reported that Mr. Musk had attempted to put Igor Kurganov, a 34-year-old former professional poker player whom he had met through Grimes, in charge of his charitable giving. Mr. Kurganov had reportedly “bonded” with Mr. Musk over their mutual devotion to Burning Man. Members of Mr. Musk’s inner circle were reportedly alarmed by the prospect of letting a Russian-born former professional gambler with no background in tech, finance, or philanthropy at that scale so close to a $230 billion fortune.

A person with direct knowledge of the situation confirmed that the F.B.I. had made initial inquiries into Mr. Kurganov’s background because of concerns about foreign interference.

(After pressure, Mr. Musk fired Mr. Kurganov from the Musk Foundation, according to The Journal.)

Neither the F.B.I. nor Mr. Birchall responded to requests for comment.

Among the Libertarians and Influencers

In L.A., Mr. Musk was taken up by Hollywood’s environmental crusaders. Since moving to Texas in 2020, Mr. Musk has become far more vocal about culture war issues, decrying “wokeness” as “divisive, exclusionary and hateful” in an interview with The Babylon Bee, a conservative satire site.

Mr. Musk has found in his new home state a group of like-minded friends, socializing quietly with a group of wealthy Austinites at that city’s increasingly busy intersection of venture capital, male self-improvement influencing and libertarianism.

He shuttles frequently between Brownsville, the border city where SpaceX is building an enormous facility and where he stays in a tiny prefabricated house in nearby Boca Chica, and Austin, where The Journal reported last year that Mr. Musk had been living in Mr. Howery’s sprawling mansion since the beginning of the pandemic. Mr. Musk also spends at least some of his time there at the Commodore Perry Estate, a luxury resort in a lavish Italianate mansion.

In January 2021, Mr. Musk hosted a party for several dozen people in Mr. Howery’s home; according to two guests, people were asked by a security guard at the door to sign nondisclosure agreements.

Among the crowd was Mr. Rogan (who would later text Mr. Musk that the two men should “throw a hell of a party” if Mr. Musk’s Twitter plans came to fruition); Grimes; Mr. Lonsdale, a Republican donor who co-founded Palantir with Peter Thiel and is funding a new university in Austin dedicated to taking “power back from ideologues”; the “Entourage” actor Adrian Grenier; the flow-state evangelist Jamie Wheal; and the media strategist turned best-selling “modern Stoic” Ryan Holiday.

These days, Mr. Musk is frequently accompanied to dinners, meetings and parties by the journalist Walter Isaacson. Mr. Isaacson, whose authorized, best-selling 2011 biography of Steve Jobs is now canonical in the tech and business worlds, is writing a biography of Mr. Musk.

But Mr. Musk isn’t always out and about in his free time.

“He doesn’t care about the trappings of wealth,” Mr. Marglin said. “He’s got insecurities. I don’t think he goes to bed thinking, ‘I’m the world’s richest man’ or even ‘Lucky me’ — only, ‘I have this plan, this mission, and everything else is in service of that.’ Unfortunately, a lot of his relationships become secondary.”

Mr. Musk, a lifelong gamer who has professed his love for first-person shooters and real-time strategy games, might be most at home on his couch. He has talked online — in tweets and in a Reddit “ask me anything” session — about playing everything from Cyberpunk 2077 (a notoriously buggy “action-adventure story set in Night City, a megalopolis obsessed with power, glamour and body modification”) to Kerbal Space Program (the goal is to send small green humanoid creatures to outer space).

In May, Mr. Musk tweeted that he had experienced the “entirety” of Elden Ring, a role-playing game which, according to the video game site HowLongToBeat.com, takes an average of 105 hours, or more than four days, to complete. When a Twitter user with around 300 followers asked Mr. Musk about his approach to the game, Mr. Musk replied in detail a couple of hours later. (“Int/Dex build, so mostly mage with some weapon skills. Shield in left hand, staff in right with rapier & claws fast switch.”)

Between the forests and castles of a $59.99 fantasy world, and the ping of a Twitter exchange, the world’s richest man seemed content.

Susan C. Beachy contributed research.