MEXICO CITY » He may have just taken on the toughest job in Cuba. Rivals at home will try to take him down. Enemies abroad will discredit him. Almost anyone with an interest in Cuba — including U.S. spies and Cuban intelligence officers — will dig through his public and private lives, rummaging for secrets or clues about his plans.

All the while, Miguel Diaz-Canel Bermudez, 52, the top contender to succeed the Castros after more than half a century of their rule, will need to display the authority of a future president while acting as if he does not want the job, maintaining the submissiveness and loyalty that the Castros require.

"It’s going to be a challenge," said Brian Latell, a former CIA agent who monitored Fidel Castro’s speeches for years and continues to track Raul Castro as an outside analyst. "The record of the Cuban revolution is littered with the names of people who were thought to be No. 3 or 2 and all of them fell by the wayside, going back to Che Guevara."

Though a stranger to many Cubans, Diaz-Canel suddenly became the chosen one when he was promoted to first vice president on Sunday as Raul Castro, 81, announced he would retire after his current five-year term ended in 2018.

Diaz-Canel replaced Jose Ramon Machado Ventura, 82, and became one of the youngest members of Cuba’s political hierarchy. His elevation raised the curtain on an epic drama that had been envisioned dozens of times over the decades. Leader after leader has been mentioned as the next president of Cuba.

Now, with the Castro era drifting to a close, all the attention is focused on Diaz-Canel, who has been thrust into what experts describe as the most scrutinized leadership role in the country since Fidel Castro took power in 1959.

Several high-placed young guns who had been auditioning for the job have been banished from government since Fidel Castro fell ill and retired in 2006. Some were accused of corruption, others of disloyalty in the form of vulgar jokes (surreptitiously recorded) about Fidel Castro’s health and Raul Castro’s political capabilities.

One of those sent packing off to "plan pajama" in an earlier purge is an old boss of Diaz-Canel’s from their days at the Union of Communist Youth: Roberto Robaina, a brilliant mathematician and former foreign minister who can now be found painting or hanging out at his Havana restaurant, Chaplin’s Cafe.

But unlike others floated as possible future leaders, Diaz-Canel has managed to be officially anointed as the successor. No one else can claim that distinction, not even Che, Fidel Castro’s right-hand man during the revolution.

And while much about Diaz-Canel remains a mystery, what is known suggests that Raul Castro made the selection. Diaz-Canel, though clearly an avowed loyalist, has little in common with Fidel Castro, in personality or outlook. He seems instead a younger, more casual version of Raul.

Like Raul, he is known for being funny and warm in small groups, and more demure when speaking to crowds. An engineer, he also shares with Raul a hefty respect for competence over ideology, and an antipathy to showy appearances. While Fidel Castro took power riding a tank into Havana, Diaz-Canel is well known within Communist Party circles for riding his bike to work when he served as the top official in the province of Villa Clara. He was born there in a lush central region of sweet-smelling mills and pristine coastal keys on April 20, 1960. His father worked for a brewery and his mother was a primary school teacher, according to someone close to the family who did not want to be identified talking about the private life of a government official.

The insider said that Diaz-Canel was a keen chess player as a child and an avid reader. He is on Facebook, looking casual in a photograph with relatives, but online there are few examples of his published commentary.

He appears to have maintained a down-to-earth approach throughout his career. After graduating from The Central University of Las Villas in 1982, he served in the military for a few years, then slowly moved up the Communist Party ranks. While others behaved like bureaucrats, he had a touch of the mod, wearing his blondish hair long and listening to rock ‘n’ roll.

"He used to be very popular among women, perceived as handsome, tall, ‘cool,"’ said Domingo Amuchastegui, a former Cuban official living outside Cuba, who briefly met Diaz-Canel early in their careers. "Even my daughter — who now lives in Ireland — remembers him as superpopular among young people in the ’80s."

Little is known about his personal life now; a woman named Lis Cuesta who works for Paradiso, a government agency that promotes tourism, said that she was his wife, closing the door of their two-story home in western Havana without offering more information. Neighbors said he lived a simple life and played baseball in a park nearby. A family insider said he has two children from an earlier marriage.

His reputation for pragmatism and competence, the traits that won him favor with Raul Castro, began to emerge more recently. As a senior official in Villa Clara and then in Holguin province, he worked closely with military leaders as they built hotels and brought in foreign investment. Analysts and former officials say he is a manager, not an innovator.

"It confirms the gradualism of Raul’s approach," said Geoff Thale, program director for the Washington Office on Latin America, referring to the modest but notable steps that Raul Castro has taken to open up the Cuban economy. "I don’t think there’s any evidence that he is someone looking to bring rapid or dramatic change to Cuba’s political or economic system."

Diaz-Canel appears to be someone who can win people to his side, as Raul Castro has done in pushing through halting efforts at reform. And like Raul Castro, Diaz-Canel is used to institutional resistance.

He overcame opposition to his appointments in Holguin, then became minister of higher education in 2009. The academic elite in Cuba initially scorned him for lacking a Ph.D. But according to several accounts, he impressed them by doing less dictating than listening.

"He was always asking questions," said a former researcher at the University of Holguin, who fled Cuba a few months ago. "He always wanted to know what was going on."

Raul Castro has mostly praised him for his hard work, and his "ideological firmness" — more than enough to attract the ire of anti-Castro Cuban Americans who have already criticized him for being a Castro protege. U.S. officials, so far, have expressed skepticism, noting that the top-down selection of a new leader does not amount to democracy.

Diaz-Canel may in fact find himself on a lonely perch if he manages to seize the top job. He will be surrounded by pent-up demands for more significant change, but without the heft attributed to the Castros and the revolutionaries who fought with them.

"He will have to watch his back," Latell said.

He will also have to improve or reinvent a Communist system built on moral rather than financial incentives, pushing thousands to flee every year for more freedom and opportunity.

"It is about redesigning the entire system, from top to bottom, saving those positive achievements, including full sovereignty, while throwing away the disastrous economic apparatus of the state, the institutional centralism and all forms of intolerance, rigidity, and the abuse of power," said Amuchastegui. "It means reaching a form of political pluralism that is more effective and representative."

Diaz-Canel has a chance to shape his own image. Of about a dozen people questioned on the streets of Havana about the new heir apparent, only half could name him.

"He’s a new generation — that’s enough for me," said Alberto, a security guard in his 40s who declined to give his full name because discussing the Cuban leadership is sensitive.

And yet, there are hints that Diaz-Canel has been quietly preparing for his new role. In a speech he gave last February to 3,500 educators from around the world at the Karl Marx theater in Havana, he talked about the need to "undergo transformation" and highlighted a maxim from Cuba’s most famous thinker, Jose Marti.

Discussing the future, Diaz-Canel reached back for a quote from 1894: "Seeing afterwards is worthless. Foreseeing is what really counts b(euro) 1/8 and being ready."

© 2013 The New York Times Company