The first Latin American pope, Argentina's Jorge Bergoglio is a theological conservative with a strong social conscience, known for his negotiating skills as well as a readiness to challenge powerful interests.
He is a modest man from a middle-class family who declined the archbishop's luxurious residence to live in a simple apartment and travel by bus.
He was also the main candidate against Cardinal Joseph Ratzinger in the 2005 conclave that elected the German to become Pope Benedict, backed by moderate cardinals looking for an alternative to the then Vatican doctrinal chief.
Described by his biographer as a balancing force, Bergoglio, 76, has monk-like habits, is media shy and deeply concerned about the social inequalities rife in his homeland and elsewhere in Latin America.
"He is absolutely capable of undertaking the necessary renovation without any leaps into the unknown. He would be a balancing force," said Francesca Ambrogetti, who co-authored a biography of Bergoglio after carrying out a series of interviews with him over three years.
"He shares the view that the Church should have a missionary role, that gets out to meet people, that is active ... a Church that does not so much regulate the faith as promote and facilitate it," she added.
"His lifestyle is sober and austere. That's the way he lives. He travels on the underground, the bus, when he goes to Rome he flies economy class."
The former cardinal, the first Jesuit to become pope, was born into a middle-class family of seven, his father an Italian immigrant railway worker and his mother a housewife.
He is a solemn man, deeply attached to centuries-old Roman Catholic traditions as he showed by asking the crowd cheering his election to say the Our Father and Hail Mary prayers.
He spends his weekend in solitude in his apartment outside Buenos Aires and is a member of well-known Argentine soccer club San Lorenzo.
"He was always a very pleasant and accessible person," said Roberto Crubellier, 65, a church employee in a downtown Buenos Aires church where Bergoglio used to go and pray.
"He used to walk from the cathedral (about 10 blocks) and he stayed, praying silently in the last rows of pews, as though he was just an ordinary guy."
In his rare public appearances, Bergoglio spares no harsh words for politicians and Argentine society, and has had a tricky relationship with President Cristina Fernandez and her late husband and predecessor, Nestor Kirchner.
Bergoglio became a priest at 32, nearly a decade after losing a lung due to respiratory illness and quitting his chemistry studies. Despite his late start, he was leading the local Jesuit community within four years, holding the post of provincial of the Argentine Jesuits from 1973 to 1979.
After six years as provincial, he held several academic posts and pursued further study in Germany. He was appointed auxiliary bishop of Buenos Aires in 1992 and archbishop in 1998.
Bergoglio's career success coincided with the bloody 1976-1983 military dictatorship, during which up to 30,000 suspected leftists were kidnapped and killed -- which prompted sharp questions about his role.
The most well-known episode relates to the abduction of two Jesuits whom the military government secretly jailed for their work in poor neighbourhoods.
According to "The Silence," a book written by journalist Horacio Verbitsky, Bergoglio withdrew his order's protection of the two men after they refused to quit visiting the slums, which ultimately paved the way for their capture.
Verbitsky's book is based on statements by Orlando Yorio, one of the kidnapped Jesuits, before he died of natural causes in 2000. Both of the abducted clergymen suffered five months of imprisonment.
"History condemns him. It shows him to be opposed to all innovation in the Church and above all, during the dictatorship, it shows he was very cosy with the military," Fortunato Mallimacci, the former dean of social sciences at the Universidad de Buenos Aires, once said.
His actions during this period strained his relations with many brother Jesuits around the world, who tend to be more politically liberal.
Those who defend Bergoglio say there is no proof behind these claims and, on the contrary, they say the priest helped many dissidents escape during the military junta's rule.
His brother bishops elected him president of the Argentine bishops conference for two terms from 2005 to 2011.
In the Vatican, far removed from the dictatorship's grim legacy, this quiet priest is expected to lead the Church with an iron grip and a strong social conscience.
In 2010, he challenged the Argentine government when it backed a gay marriage bill.
"Let's not be naive. This isn't a simple political fight, it's an attempt to destroy God's plan," he wrote in a letter days before the bill was approved by Congress.
Bergoglio has been close to the conservative Italian religious movement Communion and Liberation, which had the backing of Popes John Paul and Benedict as a way to revitalise faith among young people.
Milan Cardinal Angelo Scola, who was believed to have the most support going into the conclave, is also close to the movement, but has taken some distance from it as it got mired in political scandals in Italy.
Bergoglio has addressed the group's annual meeting in Rimini and presented the books of its founder, Rev Luigi Giussani, to readers in Argentina.
His support contrasted to the critical view that another Jesuit, former Milan archbishop Cardinal Carlo Maria Martini, had of Communion and Liberation during his life.
Martini died last year, leaving behind a posthumous interview saying the Church was "200 years behind the times."
Rev Gerard Fogarty, a Jesuit and Church historian at the University of Virginia, said he was "pretty sure I'd never see a Jesuit pope" and was surprised that Bergoglio had been chosen because of the criticism of his stand during the dictatorship.
The Jesuit order was founded in the 16th century to serve the pope in the Counter-Reformation and some members of the Society of Jesus, as the order is officially called, think no Jesuit should ever become pope.
In the 2005 conclave, Bergoglio emerged as the moderate rival candidate to the conservative Cardinal Joseph Ratzinger, who went on to become Pope Benedict. After that conclave, some commentators spoke of Benedict as "the last European pope" and said the Latin Americans had good chances to win the next time.
According to reports in Italian media, Bergoglio impressed cardinals in the pre-conclave "general congregation" meetings where they discussed problems facing the Church.
Bergoglio, who speaks his native Spanish, Italian and German, was promptly mentioned as a possible head of an important Vatican department but he begged off, saying: "Please, I would die in the Curia."
After the 2005 conclave, a cardinal apparently broke his vow of secrecy and told the Italian magazine Limes that Ratzinger got a solid 47 votes in the first round while Bergoglio got 10 and the rest were scattered among other names.
Votes began to switch in the second voting round the next morning, pushing Ratzinger's count to 65 and Bergoglio's to 35. Limes said the Argentinian was backed by several moderate German, U.S. and Latin American cardinals.
The third round just before lunch went 72 for Ratzinger and 40 for Bergoglio, according to Limes, and the German cardinal clinched it on the fourth round that afternoon with 84 votes.
Bergoglio's tally sank in the fourth round to 26, indicating some supporters had jumped on the Ratzinger bandwagon. "Some apparently concluded this was the way the Holy Spirit was moving the election," one cardinal said after the vote.