ATHENS — Underestimating Kyriakos Mitsotakis has been something of a national sport in Greece.
“Koulis,” his detractors spit out, using a common diminutive of his first name that is usually reserved for children, as they mock a barely noticeable lisp.
But after sweeping to victory in a general election on Sunday, it seems Mr. Mitsotakis, the leader of the center-right New Democracy party, may have the last laugh.
His ascent to become Greece’s prime minister is testament to his tenacity, and to the radical shifts the country’s political system has undergone amid a decade of extreme financial hardship and the ensuing recasting of political alliances.
It is also a striking resurgence for a mainstream political party at a time when European center-right parties are struggling to win elections convincingly and form governments without coalition partners.
The youngest of former Prime Minister Konstantinos Mitsotakis’s four children, Mr. Mitsotakis, 51, will have to convince a sizable chunk of the Greek population that he is up to the task of leading this exhausted nation into better times.
Mr. Mitsotakis, who was quickly sworn in on Monday and was expected to name his cabinet later in the day, will need to win over those who believe he lacks the competence to deal with the complexities of Greece’s huge economic and social challenges.
It may not be easy.
“He has the brain of a 5-year-old,” a group of young men drinking iced coffees in the northern town of Veroia said almost in chorus just after Mr. Mitsotakis made a campaign stop there. But they couldn’t explain why they thought that, and just cited the candidate’s mannerisms: “Have you seen how his eye twitches?”
Mr. Mitsotakis earned a bachelor’s degree at Harvard and a master’s at Stanford before returning to Harvard for a master’s in business administration. He worked at Chase Investment Bank and McKinsey and Company, a consulting firm, in London, before deciding to try his hand at politics.
He says that his last name helped him with his first election as a member of Greece’s Parliament, but that, if anything, it has increasingly been a burden. “I don’t see people voting for me for coming from a political family,” he said in a recent interview. “I see people voting for me despite me coming from a political family.”
Yet it may be fair to say that he might never have become prime minister had he not been his father’s son. Liberals in Greece are considered something of an oddity, and hardly ever make it into Parliament.
“His family name and connections gave him a path to politics,” said Nick Malkoutzis, editor of the economic analysis website MacroPolis. “But as leader of New Democracy, he has carved out his own space, advocating liberal policies that until recently were anathema to Greek voters and politicians alike.”
“It’s true neocommunist style,” Mr. Mitsotakis said, “and I simply laugh about these comments coming from someone who hasn’t worked a day in his life and took 10 years to graduate from university.”
Mr. Tsipras completed a bachelor’s degree in civil engineering in 2000, about eight years after enrolling in university, and went on to earn a master’s in urban planning. He briefly worked in the construction industry, but he became involved in youth politics while still at university and quickly pursued that full-time.
Mr. Mitsotakis originally faced significant internal opposition to becoming New Democracy’s leader three and a half years ago. As someone who supports private enterprise and has voted in favor of L.G.B.T. rights and a less stringent approach on migration, Mr. Mitsotakis had to win over the party’s traditionalists, conservatives and right-wingers who espouse nationalist positions and are largely anti-gay and pro-church, while also often supporting a more interventionist state in citizens’ lives.
But the party needs him, too. With racist, populist and anti-Semitic commentary common among New Democracy’s older guard, Mr. Mitsotakis ultimately came to be seen as someone who could reform the party and improve its image to make it electable.
“If the party is a broad church, then it only has one priest,” Mr. Mitsotakis said. “It was my job to keep it united and at the same time to ensure that I transform it into a modern liberal party.”
It will be a tall order, especially when pushing through unpopular measures such as evaluating the performance of civil servants.
“Mr. Mitsotakis’s premiership will be defined by whether he can show the necessary leadership skills to seize the moment, including vis-à-vis his own party,” said Mr. Malkoutzis, the MacroPolis editor. “That will be where Mitsotakis will have to weigh things up: whether the importance of a reform outweighs its political costs.”
It will take deft leadership to keep the discipline after this watershed victory, and some of Mr. Mitsotakis’s biggest challenges could come from within his party, where entrenched factions continue to support vested interests.
Then there is his personal style, a far cry from that of his peers. In this land of hyper-macho retail politics, Mr. Mitsotakis makes no secret of being an outlier. He drinks green tea and wears a lucky charm bracelet, causing some of his colleagues to roll their eyes.
When he and his wife, the former Deutsche Bank executive and entrepreneur Mareva Grabowski-Mitsotaki, separated, they did so publicly, becoming a rare high-profile Greek political couple to admit being on the rocks. They got back together five years later, and she helped him campaign alongside their three children.
Mr. Mitsotakis has had trouble shaking accusations of corruption against him and his wife, which have never been proven in court but have nonetheless been used at critical junctures against him by his political opponents.
Yet a worn-down electorate that has endured 10 years of record-high unemployment, failed social services, diminished salaries and pensions, and the constant scorn of Europe has decided to take a chance on Mr. Mitsotakis.
At the party headquarters one recent morning, young experts with doctorates from some of the world’s best universities rubbed shoulders with smoking, cursing party apparatchiks, as three Greek Orthodox priests visited. It was an apt snapshot of this time of change for New Democracy, and for Greece, that Mr. Mitsotakis hopes to oversee.
On Friday, his last day of canvassing, a speeding motorcade took him through the fields of northern Greece to shake the hands of supporters in towns that are traditional strongholds.
In Pieria, he spoke to a crowd of a couple of hundred. Families had dressed up for the occasion, babies were kissed and selfies taken in the scorching afternoon heat.
But while the crowd seemed pleased to see him, his understated tone and gentle oratory appeared to do little to fire up his supporters. It was the sort of lukewarm reception seen elsewhere on Mr. Mitsotakis’s campaign trail, where he seemed to perform better in intimate discussions with voters.
“He’s our best hope for a better future,“ said Irini Zoe Mastrothymiou, a 35-year-old party member. “He’s very likable,” she added, occasionally turning to look at him as he spoke.
Mr. Tsipras, whose fiery oratorical style echoes that of Greek leaders of yore, knew that Mr. Mitsotakis’s inability to stir public passion was a sore point, and he tried to capitalize on it. At his final speech in Athens on Friday, he told an adoring crowd of thousands that whatever Mr. Mitsotakis and New Democracy did, “they can only thrive in studios.”
“They can’t have a rally like this one,” he said. “They can’t experience the true love of simple people.”
But Mr. Mitsotakis’s election could signify a return to lower-key politics.
“There’s a big advantage in people underestimating you,” Mr. Mitsotakis said with a small smile. “I don’t mind that. I have a job to do, and I have a lot of confidence in my abilities.”