London (CNN) Boris Johnson's sister once said that as a child, he wanted to be "World King" when he grew up.

Now one of the most divisive politicians of his generation has fulfilled one lifelong dream and will become the United Kingdom's prime minister on Wednesday.

The governing Conservative party announced the result of its leadership contest Tuesday and -- in what many believed was a foregone conclusion -- his opponent, Jeremy Hunt, failed to turn around the Johnson juggernaut.

The crucial question being asked in the UK, at a critical moment in the nation's history, is what exactly drives this man? The best way to answer this is to understand exactly why he is so divisive.

First, there's his personal style. Johnson's chaotic way of doing politics offends as much as it enthralls. He has a history of making seemingly thoughtless comments, such as saying that women who wear Islamic face veils look "like letterboxes" or calling people from the British Commonwealth "flag-waving piccaninnies" with "watermelon smiles."

Nicky Morgan, a Conservative Member of Parliament and former Cabinet minister, sees how this could be a hindrance for Johnson when he takes office and has to face an electorate beyond his own party.

"I think he recognizes now that what he says causes a reaction," says Morgan. "He will still be asked about comments he's made in the past and he probably wants to move on. But the fact is in today's era, it's hard to move on."

But he can also be charming and makes great efforts to win people over -- especially in person.

Harry Mount, a journalist who used to edit Johnson's columns when he was a star writer at the Daily Telegraph, explains that Johnson is "great at making you feel good in public." Despite not having worked together for more than a decade and never really having been his boss, Mount says that to this day, Johnson "greets me with a 'cripes, it's my boss,' which is flattering for me as strangers think 'the bald guy must be powerful.'"

Boris Johnson launches his Conservative Party leadership campaign in June 2019.

Hero of the Brexiteers

This ability to flatter and make others feel liked goes some way to explaining how Johnson managed to win two terms as mayor in London, where voters historically tilt toward the UK's center-left Labour party.

Second, there's his politics -- and his political ambition. Johnson played the decisive role in making Brexit happen. In 2016, under immense pressure from the then-prime minister David Cameron to back the Remain campaign, Johnson broke ranks and backed Brexit at the last minute. This has made him the hero of the Brexiteers.

"Boris has that undefinable quality of leadership. He can persuade people to back him and go in a direction that they may not have initially supported," says Jacob Rees-Mogg, a longstanding Euroskeptic and Johnson supporter. "Only someone with his kind of optimism can get people behind Brexit."

But others think that Johnson's decision to lead the Brexit campaign was nothing more than a deliberate political move. Morgan, a Remain supporter, explains that the suspicion among some is Johnson "did this knowing that it would potentially, eventually, burnish his leadership credentials."

It's no secret that ending up in high office was always Johnson's aim. Mount says "it was always clear that he saw journalism as a ringside seat for the main contest, which he wanted to star in."

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'Doesn't do boring'

It's this naked ambition that brings us to the third and most important reason that Johnson divides opinion: his personal qualities, morality and suitability to do the job.

"The truth about Boris is that he works extremely hard. He gets up at 5 a.m., devours newspapers and would be on the phone by 6:30 a.m. wanting to discuss the day," says Guto Harri, who served as Johnson's director of communications while he was London mayor. "His approach is very much like a journalist. He cuts to the chase very quickly, spotting the relevant detail and seeing the wood from the trees."

This is not a characterization that Simon Heffer, under whom Johnson worked at the Telegraph, agrees with. "He's utterly selfish, completely oblivious to the sensitivities and needs of others and entirely unprofessional," Heffer recalls.

"We saw this when he was mayor and he needed numerous deputies because either he was too lazy, not capable, or couldn't be bothered with the detail of what was required to do the job properly."

There are no shortage of stories about Boris Johnson's personal life.

Two very different views of the same person. However, it's entirely possible that both are true. "It's wrong to say he has a short attention span or that he's lazy. Give him a difficult bit of ancient Greek and he's happy as Larry," explains Mount. "It's the important stuff he finds boring and that will be difficult. He's not going to fall over and hit the nuclear button with his arm. But he does get bored and he doesn't do boring."

That's the chaotic bit; the altogether more troubling question for some is on the moral values of a man on the precipice of power.

There's no shortage of stories about Johnson, from lurid allegations about his personal life, including affairs, to being sacked from an early journalism job for fabricating a quote. Perhaps worst of all, a recording exists of Johnson appearing to be complicit in a plot to have a journalist beaten up. The allegations prompted BBC journalist Eddie Mair to accuse Johnson of being a "nasty piece of work" to his face in an interview. In the interview with Mair, Johnson brushed off or dismissed the allegations, though was indirect in his responses.

During his time as foreign secretary, Johnson's loose words were used as proof by Iran that jailed British-Iranian Nazanin Zaghari-Ratcliffe had engaged in "propaganda against the regime." Johnson later publicly apologized in the House of Commons , saying that his comments should have been clearer.

Another example of Johnson's questionable decision-making came earlier this week, when he failed to defend Kim Darroch, the UK's ambassador to Washington, following the leak comments in which Darroch was critical of US President Donald Trump. It has since emerged that Johnson's lack of support prompted Darroch to resign.

"When you look at the appalling response he gave to the Kim Darroch question, you see how lacking in integrity and leadership he is," Heffer says. "To say Johnson's character is deeply flawed is like saying water is slightly wet. If he becomes prime minister he will be the man most deficient in probity ever to hold the post."

CNN reached out to Johnson's team for comment multiple times but did not receive a reply.

How Johnson may win

How can it be then, that a man so divisive is trouncing his rival so spectacularly?

One word: Brexit. The UK has been stuck in its Brexit crisis for over three years now. Jacob Rees-Mogg blames this failure on a government that has been dominated by people whom he suspects never really wanted to leave the EU. "To deliver Brexit needs a Brexiteer," Rees-Mogg explains.

"There are two approaches. One is that Brexit is a problem to be managed. Then there's the Boris approach, which is that Brexit is a huge opportunity."

The single biggest reason Brexit hasn't happened yet is that the UK's political class can't decide what it wants. The Withdrawal Agreement -- commonly called May's Brexit deal -- failed to satisfy both the Europhile and Euroskeptic wings of not only the Conservatives, but across the lawmakers that sit in the UK's House of Commons, who need to ratify any deal with Europe.

Given that May has been governing without a parliamentary majority since the 2017 election, this lack of consensus meant that, without a compromise from Brussels or buying off opposition votes, May's deal was always doomed.

Boris Johnson and rival Jeremy Hunt during a televised leadership debate.

That very same fate could await Johnson.

'Keen young puppy dog'

Johnson's pledge to take the UK out of the EU on October 31 "do or die" has excited Brexiteers. His pledge to threaten Brussels with walking away without a deal and withhold the nearly $50 billion the UK owes Europe, unless Europe agrees to renegotiate May's deal, is catnip to a certain type of Conservative.

His supporters sincerely believe that this approach will work. "Like Reagan, Boris has a positive view of governing. If you think that things can be achieved then you are likely to try them and you are likely to inspire people that it's worth striving for," says Rees-Mogg.

"If you look at the great political leaders, they have always been optimists. The ones who don't work are the gloom buckets like poor old Gordon Brown [the former Labour prime minister, who lost the 2010 election]."

But the problem Johnson faces isn't just uniting people in his own party, nor across the country. There are, of course 27 other EU member states, all of whom have a say on Brexit. "In Brussels, Boris is seen as the anti-Christ," says a European diplomatic source.

It's not just because of his pro-Brexit, anti-EU rhetoric. Johnson used to work as a journalist in Brussels, where he made few friends.

Bill Newton Dunn, a Liberal who has sat in the European Parliament since 1979, recalls: "My memory is that he was a very keen young puppy dog, eager to please. He wanted to get stories or embellish them to try to get ahead. He was less bothered with the truth."

The stories Dunn refers to include such hits as the EU wanting to ban curvy bananas or claims that an EU official was so well remunerated, he could afford to live in a chateau on the outskirts of Brussels. All tremendous fun and all painting a picture of a lavish, interfering European superstate. If only either story were 100% accurate, rather than embellishments on grains of truth.

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Jean Quatremer, a French journalist who overlapped with Johnson in Brussels, has written that Johnson invented an entire genre of journalism, commonly referred to as "euromyths".

The manner in which Johnson campaigned for Brexit was not a million miles from the euromyth style: who can forget the extraordinary -- and false -- claim that the UK was sending £350 million ($439 million) a week to Brussels?

Ever since May's Brexit deal was voted down for the third and final time on March 29, officials in Brussels have made clear they no longer see the UK as a reliable negotiating partner. That's unlikely to change.

Come October, some in Brussels think Johnson will desperately try to avoid no deal and attempt to sell a repackaged Withdrawal Agreement to his hardline Brexiteers.

"Does Boris, a man who has spent his entire career getting ready for this moment, want to be the shortest-serving prime minister in history? Because that's what will happen if he drags the UK off a cliff," says one EU source

The future

All of this raises the most important question for the residents of the UK: what will a Johnson premiership actually look like?

He enters office at a time when politics is fluid. It's not just the Brexiteers who have their tails up. People who have been campaigning to scrap Brexit ever since 2016 are more confident than ever that it can now be stopped.

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When you consider that his own party has mixed views on Johnson, the 48% of people who voted remain are even more worried about PM Johnson.

Hugo Dixon, a Remainer who happens to be one of Johnson's oldest friends, shares this concern. "Starting with a bit of ambition is fine, but it has to be with the aim of doing something good. And my worry with Boris is that he is heading down a path that is bad for the country."

Dixon will not be alone in this view, either in the Commons or in the country at large. And if Johnson fails to reconcile both, his days in office could be numbered from day one.

One of the great unknowns is which version of Johnson emerge as PM -- the liberal London mayor or the post-Brexit populist. For a man who has for so long lived in the spotlight, we have very little idea of what goes on underneath his blond mop of hair.

The reality might be that Johnson's fate, ultimately, is not in his own hands. If he is to take the UK out of the EU on October 31 with a new deal, then he has about two months to convince Brussels it needs to renegotiate something that took two years to agree.

If he tries to take the UK out without a deal, he might find that political gravity takes over as parliament does everything it can to stop it. And, should Johnson push hard enough, he might find that members of his own party are willing to bring down his government and force a general election.

Whatever happens, it's going to be a steep learning curve for the boy who always wanted the top job. If it goes right, he will be the man who united the country and delivered Brexit. If he gets it wrong, he might be ousted from office in a matter of months, making him an even shorter-serving leader than that poor old "gloom bucket," Gordon Brown.