Pope Francis is the first ever from the Americas, an austere Jesuit intellectual who modernised Argentina's conservative Catholic church - he is also known for travelling on the bus and cooking his own food.
Formerly known as Jorge Bergoglio, he is described as a humble man who denies himself the luxuries that previous Buenos Aires cardinals enjoyed.
The 76-year-old is known for travelling on public transport, cooking his own meals, living in a modest home with a small stove for heating and regularly visiting Argentine slums.
Pope Francis considers social outreach, rather than doctrinal battles, to be the essential business of the church.
He accused fellow church leaders of hypocrisy and forgetting that Jesus Christ bathed lepers and ate with prostitutes.
"Jesus teaches us another way: Go out. Go out and share your testimony, go out and interact with your brothers, go out and share, go out and ask.
"Become the Word in body as well as spirit," Bergoglio told Argentina's priests last year.
Bergoglio's legacy as cardinal includes his efforts to repair the reputation of a church that lost many followers by failing to openly challenge Argentina's murderous 1976-83 dictatorship.
He also worked to recover the church's traditional political influence in society, but his outspoken criticism of President Cristina Kirchner couldn't stop her from imposing socially liberal measures that are anathema to the church, from gay marriage and adoption to free contraceptives for all.
"In our ecclesiastical region there are priests who don't baptise the children of single mothers because they weren't conceived in the sanctity of marriage," Bergoglio told his priests.
"These are today's hypocrites. Those who clericalise the Church. Those who separate the people of God from salvation. And this poor girl who, rather than returning the child to sender, had the courage to carry it into the world, must wander from parish to parish so that it's baptised!"
This sort of pastoral work, aimed at capturing more souls and building the flock, was an essential skill for any religious leader in the modern era, said Bergoglio's authorised biographer, Sergio Rubin.
But Bergoglio himself felt most comfortable taking a very low profile, and his personal style was the antithesis of Vatican splendor.
"It's a very curious thing: When bishops meet, he always wants to sit in the back rows. This sense of humility is very well seen in Rome," Rubin said before the 2013 conclave to choose Benedict's successor.
Bergoglio's influence seemed to stop at the presidential palace door after Nestor Kirchner and then his wife, Cristina Fernandez, took over Argentina's government.
His outspoken criticism couldn't prevent Argentina from becoming the Latin American country to legalise gay marriage, or stop Fernandez from promoting free contraception and artificial insemination.
His church had no say when the Argentine Supreme Court expanded access to legal abortions in rape cases, and when Bergoglio argued that gay adoptions discriminate against children, Fernandez compared his tone to "medieval times and the Inquisition."
This kind of demonisation is unfair, says Rubin, who obtained an extremely rare interview of Bergoglio for his biography, the "The Jesuit."
Many Argentines remain angry over the church's acknowledged failure to openly confront a regime that was kidnapping and killing thousands of people as it sought to eliminate "subversive elements" in society.
It's one reason why more than two-thirds of Argentines describe themselves as Catholic, but fewer than 10 percent regularly attend mass.
Under Bergoglio's leadership, Argentina's bishops issued a collective apology in October 2012 for the church's failures to protect its flock.
But the statement blamed the era's violence in roughly equal measure on both the junta and its enemies.
Bergoglio twice invoked his right under Argentine law to refuse to appear in open court, and when he eventually did testify in 2010, his answers were evasive, human rights attorney Myriam Bregman said.
At least two cases directly involved Bergoglio. One examined the torture of two of his Jesuit priests - Orlando Yorio and Francisco Jalics - who were kidnapped in 1976 from the slums where they advocated liberation theology.
Yorio accused Bergoglio of effectively handing them over to the death squads by declining to tell the regime that he endorsed their work. Jalics refused to discuss it after moving into seclusion in a German monastery.
Both men were freed after Bergoglio took extraordinary, behind-the-scenes action to save them - including persuading dictator Jorge Videla's family priest to call in sick so that he could say Mass in the junta leader's home, where he privately appealed for mercy.
His intervention likely saved their lives, but Bergoglio never shared the details until Rubin interviewed him for the 2010 biography.
Initially trained as a chemist, Bergoglio taught literature, psychology, philosophy and theology before taking over as Buenos Aires Archbishop in 1998.
He became cardinal in 2001, when the economy was collapsing, and won respect for blaming unrestrained capitalism for impoverishing millions of Argentines.