When the future king of the world deigned to meet with Simon Murdoch, he led with a threat. It was 1998 and Jeff Bezos, the head of a fledgling American e-commerce company called Amazon.com, had invited the British entrepreneur to an impressive duplex hotel suite in Kensington to propose a deal.

Amazon, Bezos explained, would soon be expanding into the UK, which would mean competing with Murdoch's own company, Bookpages. But might it not be better for the two firms to work together? Might both make so much more money if Amazon bought Bookpages?

"That was a veiled threat, yes of course," recalls Murdoch, who now spends his work hours searching for the next Bezos as head of the London-based venture capital firm Episode 1.

"That was one of the key points we took away from the meeting: 'Consider this carefully or prepare to be squashed'. He said that to us not being aggressive or nasty, just being factual... and I know for a fact they talked to at least one of our competitors. He is a very ruthless businessman... he is the smiling assassin."

Today Amazon is a behemoth, and Bezos has knifed his way to a net worth of around $200bn (£146bn). That fortune is bigger than the entire market capitalisations of Nike, McDonald's, Starbucks and Goldman Sachs – making him the world's wealthiest man by such a margin that he kept that title even after paying out the largest divorce settlement in history ($38bn) to his first wife MacKenzie.

Not that he is satisfied. On Tuesday, he announced he was standing down as Amazon chief executive. In recent years Bezos has intensified interests in other areas, including his rocket company Blue Origin and philanthropic climate work.

"Right now I see Amazon at its most inventive ever, making it an optimal time for this transition," Mr Bezos said in a quote accompanying its quarterly results.

But Amazon continues to expand relentlessly (one of his favourite words), ambushing British supermarkets last year with the news that it would start delivering groceries in the UK. Like industrialists of yore, Bezos has his own newspaper, the Washington Post, and through his space company Blue Origin he even hopes to shape humanity's future.

Last year he testified to Congress alongside Facebook's Mark Zuckerberg, Alphabet's Sundar Pichai and Apple's Tim Cook. Bezos was grilled about accusations that Amazon exploited sales data from companies on its third-party marketplace to devise and launch its own rival products (which it firmly denies).

Bezos cuts a very different figure to his fellow tech barons. Whereas Zuckerberg, Twitter's Jack Dorsey and Tesla's Elon Musk often broadcast their thoughts on social media, Bezos rarely gives interviews, does not appear on TV and does not even join his own earnings calls.

The differences do not stop there: Bezos is not only among the oldest at 56 (20 years beyond Zuck) but also the least outwardly geeky. He does not boast of being an "engineer" or a "coder", let alone a "hacker". His company began with a business plan, not a revolutionary algorithm or an addictive piece of software, and now has a reputation among tech workers for elevating hard-nosed corporate sharks over unkempt eggheads.

And yet for the first 26 years of his life, Bezos too seemed like a typical nerd. Growing up in Texas and Miami, he built home-made versions of toys he could not afford, appeared in a documentary about gifted children, made his siblings read Lord of the Rings at his own summer camp and spent hours playing a Star Trek game on his school's rented mainframe time. So what transformed a man once bracketed alongside the "fuzzy-cheeked geek[s]" of the dotcom boom into Earth's most prosperous human?

Born Jeffrey Jorgenson in 1964, Bezos never knew his biological father, whose drinking drove his mother Jacklyn to take her baby and run just 17 months later. His adoptive father (his real one, he says) was Mike Bezos, a Cuban refugee who arrived in the US alone at age 15. Later, he studied computer science and worked for technology firms, but at 26 he made the fateful decision to accept a job at a New York hedge fund – albeit one founded by a fellow computer scientist.

Bezos's four years at DE Shaw may well have changed the world. To start with, he met MacKenzie, then a researcher at the firm, and probably absorbed some of Wall Street's ethos. Perhaps more importantly, it was while managing Shaw's new internet investments and analysing the nascent e-commerce sector that Amazon began to take shape in his head. In 1994 he left, driving with his wife across the country to Seattle so that they could be close to a massive book distribution hub.

Simon Murdoch came on board four years later, leading Amazon's new UK arm (and convincing its sceptical American leadership that British consumers would trust "Amazon.co.uk" more than "Amazon.com/uk"). The 59-year-old Yorkshireman, who has since sold two more companies to Amazon, remembers Bezos as an "awesome individual" unfazed by his then net worth of $4bn.

"He seemed very authentic – super smart, very passionate. We instantly felt this was somebody who was charismatic and that we wanted to work with," Murdoch recalls. He also remembers the occasional "poisonous" remark and a brutal work schedule which caused some employees (including Murdoch) to burn out.

Mostly, though, he saw the qualities that secured Amazon's victory: a gift for inspiring employees by building a distinctive office culture, an obsession with recruiting exceptional people (each early hire had to be better than the last), and a willingness to delegate that would later allow Amazon to diversify itself far more than the comparatively centralised and narrowly-focused Facebook.

Even so, it took another decade and a half for those plans to come to fruition. Amazon's share price lagged behind its rapid customer growth as Bezos, in what is now a famous and lauded strategy, ploughed all its profits back into expansion. Just like Uber and WeWork today, it was cited by analysts as evidence that the stock market had lost its head.

"The narrative with Bezos and Amazon then was: 'what's wrong with the investment community that they continue to fund a business that loses money with every transaction?" says Steven Weber, a professor of technology and global politics at the University of California, Berkeley. "[Investors believed] that it was playing the game of the dotcom era – pay the cost to acquire customers, and once we have that market owned we'll raise profits."

What changed that, Weber says, was Amazon Web Services (AWS). Spun off from Amazon's own internal cloud computing division in 2006, it initially seemed a strange venture to many. "Why should a company that has set its heart on being the best e-commerce business also try to become the best in server technology?", Murdoch recalls.

Over the next ten years AWS became the backbone of the internet, letting smaller companies rent computing power as easily as they might rent electricity (Bezos has compared it to the first utility companies). In 2015 it made its first profit, transforming Amazon's finances and triggering a gigantic stock rally which made Bezos's fortune and which continues to this day.

For Murdoch, AWS epitomises the audacious Tao of Bezos. "He doesn't really care what other people think, and he doesn't care about Wall Street either," he says. "Most chief executives would listen to Wall Street and wouldn't make such a bold decision as AWS. It's a good example of him being a long-term strategic thinker."

The turnaround confirmed Bezos as a cult figure among business strategists, who often cite his regular shareholder letters. It coincided with a transformation in his personal image, most visible in widely-discussed 2017 photos of his suddenly bulging muscles and his high-profile affair with the actress and TV anchor Lauren Sánchez.

It also seems to have given him the time to return to his teenage space obsession, funding and personally joining an oceanic expedition to recover the sunken rocket engines that threw Neil Armstrong towards the moon.

The deca-billionaire will therefore no doubt go before Congress with deep reserves of swagger. Some members might raise an eyebrow at Amazon's estimated 38pc share of US e-commerce and its 32pc share of the cloud computing market – to say nothing of his 1999 statement that "a level playing field" is not desirable "when you’re marching into battle". But Weber argues that AWS, which is a key vendor to the US government and military, is a political ace in the hole as well as a financial one.

"If I were Bezos I might want to say: 'the thing I am most proud of is actually AWS'," he says, imagining the tycoon's pitch."'It has lowered the barrier for entrepreneurship in the US, and created the possibility for smaller companies'. How many jobs has Facebook created?'...

"Americans love that kind of audacity if it works out. If it doesn't work you’re a moron and a criminal. If it does work out you’re a genius and a visionary."

With an average wealth increase of $12m every hour, it would be hard to argue with the results.