One of "God's Marines" is now Pope, with Argentine Jorge Mario Bergoglio today becoming the first Jesuit elected to lead the world's Catholics.

Jesuits are labelled "God's Marines" or Catholic ''storm troopers'', in recognition of their 16th-century founder Ignatius of Loyola, who had a military background.

The Society of Jesus (more commonly known as Jesuits) demands four vows: poverty, chastity, obedience to Christ, and obedience to the Pope.

Its purpose is the propagation of the Catholic faith by any means possible.

A Spanish nobleman, Ignatius of Loyola was set on a career as a professional soldier, until a cannonball shattered one of his legs in 1521.

During his recovery he read religious books, fasted and prayed, then decided to become a soldier of Christ.

The Jesuits' first focus was the conversion of Muslims, then halting the spread of Protestantism.

With their military-style training, the Jesuits were feared as the "storm troopers" of the Roman Catholic Church, and led armies which recaptured large areas for it.

The goal of modern Jesuits is to spread the Catholic faith, now through missionary work and education, rather than military action.

In Latin America, Jesuits have had significant influence in the development of liberation theology, which has been controversial with Catholic theologians.

- © Fairfax NZ News