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- Australian Catholics welcome pontiff
- List: Popes of the past 135 years
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They are sometimes referred to as "God's Marines" or the church's "storm troopers" - a band of priests and missionaries who live sparse lives and are willing to accept religious orders anywhere in the world, sometimes living in extreme conditions.
The order elects its own leader, known as the Black Pope because of the black vestments worn by the Jesuits
Now, in a world first, a Jesuit has been appointed Pope in a surprise election that Australian Jesuits say could lead the Catholic Church in a new direction.
Jesuit: newly-elected Pope Francis I appears on the central balcony of St Peter's Basilica. Photo: Getty Images
It's also sparked renewed interest in a small and highly committed order that hatched from military beginnings and has only 20,000 members worldwide, of whom about three quarters are priests.
Pope Francis, who until Wednesday was known as Jorge Mario Bergoglio, made a name for himself leading a spartan life in his native Argentina.
Instead of taking up residence in a luxurious mansion that came with the job of the archbishop of Buenos Aires, he chose to live in a small apartment, prepared his own meals and eschewed a chauffer-driven car in favour of travelling by public bus.
New pope elected: white smoke emerges from the chimney on the roof of the Sistine Chapel. Photo: AP
The 76-year-old regularly visited the slums that ring Argentina's capital and spoke to the poor.
That humility and social conscience is one of the founding principles of the Society of Jesus, the liberal Catholic religious order whose members are known as Jesuits and who are required to take vows of poverty, chastity, obedience to Christ and obedience to the Pope.
They have been given the nicknames "God's Marines" or religious "storm troopers", in recognition of their 16th-century founder Ignatius of Loyola, who had a military background, as well as the Jesuits' willingness to travel throughout the world on missionary work.
Argentina's cardinal Jorge Bergoglio, elected Pope Francis Photo: AFP
Father Andrew Hamilton is a Melbourne-based Jesuit priest, one of about 140 Jesuits based in Australia. Of those, 20 were based overseas last year.
Father Hamilton said while there were many Jesuits in the Vatican, he was delighted that Pope Francis had been elected the first Jesuit pope, and that his background would stand him in good stead.
"We take a vow of poverty and that's following Jesus in his lifestyle to some extent," Father Hamilton said.
The Black Pope .... Father Adolfo Nicolas, pictured with Pope Benedict XVI. Photo: Getty Images
"Not everybody would live in the way that [Pope Francis] does. But certainly to see that ideal embodied in someone's lifestyle as conspicuously as he has done, it's a choice which distinguishes him from other people who have been in the office before. That is something which I'd be proud of in any Jesuit."
Jesuits also are known for being the intellectuals among priests.
They run top colleges and schools, including Xavier College in Melbourne and St Ignatius' College in Riverview in Sydney, which counts among its alumni federal Opposition leader Tony Abbott and former NSW premier Nick Greiner.
Meet Pope Francis
A selection of images of Pope Francis, cardinal Jorge Mario Bergoglio of Buenos Aires. Photo: AP
The Society of Jesus was founded by Saint Ignatius, the patron saint of soldiers, a Spanish knight who was set on a career as a professional soldier until he suffered a severe leg injury during battle in 1521.
During his recovery he underwent a religious conversion and decided to become a soldier of Christ.
The Jesuits' first focus was the conversion of Muslims, then halting the spread of Protestantism.
The goal of modern Jesuits is to spread the Catholic faith, now through missionary work and education, rather than military action.
The order elects its own leader, known colloquially as the Black Pope because of the black vestments worn by the Jesuits, at a conclave in Rome, where members from around the world gather to make their choice. The current leader is Father Adolfo Nicolás, of Spain.
While most Jesuits avoid clashes with the Vatican hierarchy, previous popes, including John Paul II, have taken issue with the autonomy the order appears to enjoy.
In 2007 the doctrinal office of the Vatican criticised the "erroneous ... and even dangerous writings", of a Spanish Jesuit scholar named Jon Sobrino, an advocate of Marxist-inspired theology.
Father Hamilton said, while he was not fond of the military image associated with "God's Marines", it conveyed the idea that Jesuits were ideally available for special duties.
"If there's a job to be done and somebody needs to go to far off places or to be in a place where the church isn't normally, such as an intellectual place like universities and so forth, we would be available for those ministries on the edge," he said.
He said the Pope's selection of the name Francis - after either Francis of Assisi or Francis Xavier - was an indication of the direction he intended to take.
"First of all it's a new name. He's Francis the first, and that indicates somebody who is his own man, and he will go his own way," Fr Hamilton said.
"Secondly, Francis of Assisi was notable for living extremely simply and very freely within his own life.
"Francis Xavier is a Jesuit saint who travelled to India and worked in Japan and tried to get to China and worked through Indonesia back in the 16th century, and he is again one of the people who brought faith to people. So there's a very significant direction suggested by those two names."