Pope Francis, wearing the mantle of a humble advocate for the poor while defending Catholic orthodoxy, rose from modest beginnings to become the first Latin American leader of the 1.2 billion-strong Church.
The former archbishop of Buenos Aires, Jorge Mario Bergoglio, 76, has already won hearts in his first days as pontiff with a disarmingly informal style, choosing simple vestments and preferring to walk instead of ride in a limo.
In Buenos Aires, Bergoglio lived in a small apartment instead of the archbishop's palace and took public transport, shunning the perks associated with high office.
Bergoglio, the son of an Italian immigrant railwayman, spent almost his entire career in Latin America -- far from the intrigues of the Vatican bureaucracy thought to have spurred his predecessor Benedict XVI's shock resignation.
His election is being seen as a long-overdue nod to the Church's power in Latin America, which is home to 40 percent of the world's Catholics, while in Europe, its traditional power base, it is ageing and declining.
Though haunted by criticism from leftists at home for failing to speak out during the brutal "Dirty War" when he was head of the country's Jesuits for six years, he built a reputation as a voice of conscience and advocate of the poor.
The Vatican has firmly denied claims that Bergoglio -- now the first Jesuit pope -- failed to protect two Jesuit priests who were tortured by the 1976-1983 regime, saying that he had in fact protected lives during the dictatorship.
Pope Francis is seen in Argentina as ideologically mainstream, having battled to prevent Jesuits from joining the liberation theology movement, which drew many priests into political opposition to Latin America's right-wing governments.
The first non-European pope in nearly 1,300 years was a leading voice on the side of the dispossessed in Argentina's economic crisis, and at his inauguration spoke out against destructive forces in the "advance of this world".
Like his predecessor Benedict XVI, Francis has hit out at the International Monetary Fund and at modern market capitalism -- a stance that could make him an important voice as Europe suffers under biting austerity plans.
It is in keeping with his decision to adopt the name of St Francis of Assisi, who shunned worldly comforts to work with the poor, and his leadership as a Jesuit.
The Catholic order of priests known as the Society of Jesus is committed to grassroots service as well as education, running more than 100 universities around the world.
-- Jesuits must vow obedience to pope --
Antonio Spadaro, editor of the Jesuit Catholic Civilization periodical, said the homage to St Francis of Assisi was significant because poverty "is at the heart of the Jesuit experience".
But the moderate conservative is seen as unlikely to change major tenets of Catholic doctrine on issues such as abortion, divorce and homosexuality, as well as priestly celibacy and the ordination of women.
When Argentina became the first Latin American country to permit same-sex marriage in 2010, he was furious.
"Let's not be naive," he declared. "This is not just a political struggle. It is destructive to God's plan."
But he has shown signs of more openness too. Last year he criticised priests who refused to baptise children born out of wedlock saying this was a form of "rigorous and hypocritical neo-clericalism".
Francis, taking on the leadership of a Church beset by scandal and signs of deep internal dysfunction, has drawn praise for his no-nonsense approach, and his modest style has sparked hopes for a badly needed image overhaul.
Sergio Rubin, who co-wrote a book of interviews with Bergoglio entitled "The Jesuit", said he would "renovate the Roman Curia" -- the intrigue-filled Vatican bureaucracy -- and "breathe new life into the Church".
Academic Jose Bento da Silva, an expert on Jesuits at Warwick Business School in Britain, added: "No other religious order knows how to manage a global community like the Jesuits.
"The Jesuits are strongly aligned with the Catholic Church's doctrine and famous for unsettling the hierarchy of the Church," he said.
Among hot-button issues facing the new pope is the scourge of paedophile priests and cover-ups by their superiors and a longstanding money-laundering scandal at the Vatican bank, which exposed infighting among Benedict's closest allies.
Born on December 17, 1936, Bergoglio had a brush with death as an adolescent when a severe bout of pneumonia led to an operation to remove part of his lung.
The Vatican confirmed that he had had the operation but said it was not a handicap.
Bergoglio attended the University of Buenos Aires, graduating with a masters degree in chemistry aged 22.
But he changed tack by joining the Society of Jesus and beginning his studies for the priesthood.
Bergoglio went on to attend the Philosophical and Theological Faculty of San Miguel, where he earned a degree in philosophy, and later received a doctorate in theology in Freiburg, Germany.
The new pontiff is an opera lover and a fan of literary giants such as Jorge Luis Borges and Fyodor Dostoyevsky, as well as an ardent supporter of Buenos Aires football club San Lorenzo.
He has also said he loves the tango and used to be a good dancer in his youth.
He is an early riser -- waking at 4:30 am -- which cramped his social life in Argentina, as he is in bed by 9:00 pm, two hours before most Argentinians sit down for dinner.
Becoming the first Jesuit pontiff has left some experts scratching their heads, since Jesuits are required to take a special vow of obedience to the pope.