He was a slave trader & mercenary, who 'accidentaly' killed his brother in sudden duel, then later isolated himself (he was untouchable by law, because his brother asked him a duel), before his meeting with Father Gabriel, who happened to build a mission to convert Guarani tribe. Later he followed Father Gabriel to the mission, and became a Jesuit monk. In the end of the movie, he & other Jesuits, as well as most Guarani tribe, were slaughtered by Portuguese invasion.