As creator and controlling force behind Facebook, with the intimate data of more than two billion users at his fingertips and a net worth estimated at £50 billion ($96.4b), Mark Elliot Zuckerberg is one of the richest and most powerful human beings in history.
Having reached this lofty status at just 33, he was, until recently, widely regarded as a genius capable of shaping tomorrow's world in his own image — a man of such rare talent that only a fool would bet against him one day ascending to the office of U.S. President.
What, then, are we to make of this week's extraordinary events in the U.S. Congress, where hype about Silicon Valley's boy wonder collided with cold, hard reality. Awkward, shifty and, at times, comically evasive, Zuckerberg spent two days stammering his way through hearings over his company's cavalier treatment of the public's personal information.
Ridiculed online for everything from his clammy appearance to his ill-fitting suit, the supposed Master of the Universe — who is a mere 5 ft 7 in — was even caught using a booster seat to make himself look more imposing as he gave evidence to lawmakers.
Some observers likened the hearings to the denouement of the Wizard Of Oz — when curtains are pulled back and the all-powerful wizard turns out to be a feeble old man.
So, what is the truth about this weird, squeaky-voiced billionaire? Funnily enough, Zuckerberg's own (open) Facebook page gives us a very good idea...
Tycoon in training
Zuckerberg lists his childhood home as Dobbs Ferry, a commuter town just outside New York where he grew up one of four children of a psychiatrist called Karen and a dentist called Edward, whose nickname was "the Painless Dr Z" and who worked from a surgery attached to the family home.
Edward, whose website boasts "we cater for cowards", introduced Mark to computer programming at the age of 11. Within 12 months, he'd created a program that alerted his father when a patient had walked into the waiting room.
While at boarding school, computer prodigy Mark then wrote a program that would recommend music to a user based on previous songs or albums they had listened to. Microsoft caught wind of it and offered to buy it, but he turned them down. He also turned down a lucrative job offer from the tech giant AOL in order to go to Harvard to study psychology and computer science. The rest, as they say, is history.
College social climber
The creation of Facebook was, of course, chronicled in the hit film The Social Network, which portrays "Zuck" as an insecure social climber who brutally dispensed with friends who helped build the company in its early days.
Ironically, the movie's writer, Aaron Sorkin, was once listed as one of Zuckerberg's favourite film-makers. The endorsement vanished from the young tycoon's Facebook page around the time the unflattering film came out.
For those who haven't seen it, the movie tells how Facebook was originally designed in a university bedroom. Its purpose was to allow leering, male Harvard students to rate female peers in order of their attractiveness.
One co-founder, a fellow student called Eduardo Saverin, ran the enterprise's commercial side. But he was cruelly frozen out when Zuckerberg dropped out to run the site full-time. After a lengthy legal battle, Saverin got around £750 million in compensation.
Also dispensed with were Tyler and Cameron Winklevoss, fellow undergraduates who hired Zuckerberg to program a dating website and claimed key features of their idea were then stolen and used on Facebook. They received a reported £43m in an out-of-court settlement.
Zuckerberg moved directly to Silicon Valley after dropping out of Harvard.
His journey up the local property ladder has been avidly chronicled via his own website ever since, with the billionaire sharing regular behind-the-scenes images of his comparatively modest domestic set-up.
For several years, he rented a four-bedroom house in a leafy suburb of Palo Alto — a wealthy city adjacent to San Francisco where almost every major internet firm is based — for a (by local standards) paltry £3,500 a month.
He also drove a beaten-up Honda Acura, on the grounds that it was "safe, comfortable, not ostentatious".
Finally, in 2011, he became a homeowner, spending £4m on a two-storey, five-bedroom property ten minutes from Facebook's head office (where he typically works for 60-70 hours a week).
He also upgraded his car to a Volkswagen Golf GTI, which he drives to company HQ at 8am in order to attend daily sessions with a personal trainer.
The house is fashionably decorated, with wooden floors, beige carpets, and (famously) not a single television set.
It's a pretty humble abode for one of the world's wealthiest men and supporters of Zuckerberg invariably like to observe that he has no time for the gated mansions and mega-yachts of other, more brash billionaires.
What they usually fail to mention is that Zuckerberg also spent a punchy £21m buying up all of the neighbouring houses that overlook his oh-so-humble home and its garden. And in 2014, he dropped another £75m buying up 750 acres of the idyllic Hawaiian island of Kauai, in order — one assumes — to one day build a proper Bond -villain-style residence.
The doctor wife
Aside from his trillion-dollar tech firm, Zuckerberg's wife, Priscilla Chan, is the other great legacy of his stint at Harvard. The couple met one Friday night during a beer-fuelled party at the all-male "fraternity house" where Mark lived. "He was this nerdy guy who was just a little bit out there," recalled "Cilla", as she is known to friends, in a rare interview.
History relates that they struck up a conversation while queuing for the loo: he charmed her with computer science-based "college humour", apparently.
After graduating from medical school, Priscilla, the daughter of Chinese "boat people" from Vietnam, whose family fled communism during the Cold War, moved to Palo Alto and began working at San Francisco General Hospital.
The couple moved in together in 2010, announcing this and every other formative step in their relationship via Facebook. "Now we have 2x everything, so if you need any household appliances, dishes, glasses, etc, please come by and take them before we give them away," they declared.
The wedding was in 2012, days after the launch of Facebook on the stock market minted their status as billionaires, and they honeymooned in Rome, where they were photographed in that well-known Italian destination restaurant, McDonald's.
Though fully qualified as a paediatrician, Priscilla no longer has an employer to list on social media: like many a billionaire's spouse, she devotes herself to philanthropy, running a personal charity dedicated to "advancing human potential and promoting equal opportunity".
Wacky home life
The business model of Facebook (not to mention the source of many of its recent troubles) rests on the belief that a person's character is laid bare by the sort of thing they profess to "like" on social media.
On this front, Mark Zuckerberg has declared himself a fan of the sport of fencing, the pop acts Green Day, Taylor Swift, Shakira, and Jay-Z, the movie Gladiator and the fruity and violent TV series Game Of Thrones.
He and Priscilla also try to find time in their busy schedules to cook family meals and bake bread, cakes and biscuits, and tend to celebrate special occasions by heading out to parties wearing wacky fancy dress outfits. Recent times have seen the family dress as Jedi knights, medieval warriors, and characters from the children's book Where The Wild Things Are.
What a psychologist might make of this is anyone's guess, though his appearance in front of the U.S. Congress this week suggests the real Zuckerberg is nowhere near as free-wheeling and zany as his carefully curated Facebook page suggests.
In fact, he's a man with such apparent incapacity for introspection that many have suggested he may be autistic and even close friends admit that he often looks and sounds like a robot.
In 2010, one told The New Yorker: "He's been over-programmed."
Instead of spontaneously pursuing hobbies, Zuckerberg likes to give himself annual "challenges", which he announces to his 107 m Facebook followers. They have included learning to speak Mandarin ("some members of Priscilla's family only speak Chinese and I want to be able to talk to them") and, in 2011, to "only eat meat if I killed the animal myself".
Zuckerberg was once thought to be an atheist, but now likes to share photographs of his family celebrating Jewish festivals, stating in one caption: "I was raised Jewish and then I went through a period when I questioned things, but now I believe religion is very important." Priscilla, for her part, practises Buddhism.
The doting dad
Like millions of his users, Zuckerberg is an aficionado of "sharenting" — the modern-day practice of using social media to bombard friends and acquaintances with sometimes intimate items of family news.
In 2015, he told the world that Priscilla was pregnant for the first time in a heartfelt post revealing that she'd previously suffered three miscarriages, pledging to take two months' paternity leave after becoming a father.
Their daughter, Maxima, arrived later that year. Revealing the happy news, he used Facebook to announce that he intended to give away 99 per cent of his shares in the company during his lifetime, in an effort to make the world that she grows up in a "better place".
When a second girl, August, came along last summer, Zuckerberg uploaded a similarly preachy message, welcoming his newborn to the world via an open letter that urged her to make the most of childhood by finding as much time as possible to "go outside and play".
Somewhat awkwardly, Facebook made headlines just three months later by announcing it was launching Messenger Kids, a program designed to encourage his customers' children to devote even more of their waking hours to staring at a screen.
The fifth member of the Zuckerberg clan is Beast, a dreadlocked Hungarian sheepdog acquired from a breeder in Oregon in 2011.
Naturally, the little fellow boasts his own Facebook page, with an astonishing 2.7 million followers. It contains videos of him performing a host of party tricks: dancing to rap music, barking at the Rocky theme tunes and scampering along a treadmill in his master's home gymnasium.
Although there's also footage of Beast travelling to a rural farm to try his hand at herding sheep, the pooch's days are largely spent in suburban Palo Alto, where his master can often be spotted walking him to the local park.
From time to time, like every member of the household, he's also required to sacrifice his dignity to indulge Mark's love of fancy dress. Recently, he's been photographed in everything from Star Wars outfits to faux-medieval headgear and Jewish religious attire.
Silicon Valley myth has it that Zuckerberg's wardrobe is stuck in perpetual adolescence, with his supposed outfit of choice a grey T-shirt and dark hooded top teamed with grey jeans, which he once claimed to wear daily in order to limit time wasted making "frivolous decisions", such as deciding what to wear.
In 2012, he cemented this reputation for scruffiness by turning up in a "hoodie" to pitch his multi-billion-dollar IPO share offer to Wall Street executives.
Around the same time, he was said to have worn pyjamas to a meeting with financial backers.
Zuckerberg's Facebook page reveals something subtly different, however: he frequently does put on a suit and tie — provided it helps him keep up appearances.
So it goes that he's donned formal attire to meet everyone from Barack Obama to the Pope and, of course, to appear before Congress this week. He also dressed up for his wedding.
At Facebook HQ, meanwhile, there's no official dress code.
But this trendy policy only extends so far: in a 2016 memoir, former employee Antonio Garcia Martinez claimed the male-dominated tech firm's female employees were required to "avoid clothing that 'distracted' co-workers", adding that women who wore "revealing" dresses were "read the riot act".
His foul mouth
However carefully he might curate his public Facebook page, Zuckerberg hasn't always behaved like a cuddly family man.
In the early days, his business card read "I'm CEO, bitch," and, in private messages to colleagues, several of which became public during litigation, he described the site's users as "dumb f**ks" for handing over personal information to him for free.
Time would, of course, prove him right: today, his 18 per cent stake in the firm provides him access to intimate details about the private lives of its two billion users. Every message they send, photograph they share and place from where they update their profile are stored on the company's computer systems.
For handing over this valuable resource, Facebook users have been paid precisely nothing.
Whether Zuckerberg appreciates the responsibilities this ought to confer on him is hard to gauge.
During the recent crisis over the firm Cambridge Analytica harvesting data from Facebook users — which knocked US$60b ($81.3b) off the value of the company's shares — he took four days to make any statement and a further 24 hours to issue something approaching an apology.
So convinced is Zuckerberg of his own brilliance that there is mounting speculation he's thinking of one day mounting a bid for the U.S. presidency.
To this end, he recently used Facebook to announce that he's spending the year on a so-called "listening tour" of all 50 U.S. states, ostensibly to listen to Facebook users, voters and local lawmakers, hiring Charles Ommanney, a photographer for the Bush and Obama campaigns, to document the exercise.
His exact political allegiances are unclear: though undoubtedly a social liberal who vigorously supports gay rights and has been highly critical of Donald Trump's policy towards immigrants and racial minorities, Zuckerberg is also thought to be fiscally conservative and his own company's tax affairs are a case study in rapacious capitalism.
He has appeared at fundraisers with the Republican governor Chris Christie in his native New Jersey, too, though the occasion was staged to mark his decision to donate US$100m to local schools, rather than to represent a political endorsement.
Although he now employs Barack Obama's former campaign manager David Plouffe and his pollster Joel Benenson, and is certainly rich enough to run for the White House, he has repeatedly — for public consumption — denied any plans to run for office.
Perhaps that's just as well — for, as this week has shown, all the money in the world hasn't helped this awkward young billionaire avoid a political car crash.