BUENOS AIRES -- As an undocumented immigrant, Olga Cortez spent a decade toiling in sweat shops, hiding from the law and wondering if her three children were ever going to have a future in this city. So when the man in a black cassock and carrying a small valise got off the bus and walked into the soup kitchen, she found it hard to believe.

“When he opened up his bag he had that tall hat in it,” said Cortez from Bolivia. It was the hat Catholic cardinals wear, and the man wearing it was Argentina’s most powerful religious leader: Jorge Mario Bergoglio. He was there to baptize her daughters.

Bergoglio, 76, became Pope Francis last week in an event that has thrilled the hemisphere and raised questions about his role in Argentina’s troubled past. During his first days as pope, Bergoglio’s humor-filled homilies and stubborn austerity — he refused to ride in the papal limousine, wear a gold cross or traditional red slippers — have surprised many. But in Buenos Aires, people are used to seeing the dry-witted cardinal riding the subway, preaching in slums and ministering to the country’s marginalized.

Bergoglio’s youngest sister, María Elena Bergoglio, 65, said she always called him “His Holiness” in jest, but no one expected him to become the world’s most eminent Catholic.

“He’s always been so modest,” she said.

When she saw him on the balcony of the Vatican on Wednesday as thousands screamed “Long live the Pope!” she was stunned. “I thought ‘You poor wretch, God has pulled a fast one on you.’ ”

Bergoglio became archbishop of Buenos Aires in 1998 and was named cardinal in 2001. The presidential palace can be seen from the steps of the city’s cathedral, and Bergoglio’s sermons often seemed aimed at the couple inside, President Cristina Fernández de Kirchner and her late husband and predecessor Néstor. Bergoglio preached about the dangers of concentrating power and weakening democratic institutions, and he quietly backed efforts to block Kirchner allies in state races. Néstor Kirchner, who died in 2010, accused then-Cardinal Bergoglio of being the true “leader of the opposition.”

But Bergoglio dedicated much of his time to those without a voice. In 2008, he began collaborating with Fundación Alameda, a charity that rescues victims of human trafficking pressed into labor as prostitutes and sweatshop workers. Alameda staff said Bergoglio would often come in the dead of night to help women escaping violent brothel owners find shelter. He also threw his support behind controversial whistleblowers who claimed the police and powerful politicians were involved in the sex trade. In 2011, he held Mass in front of a sweatshop that had burned down five years earlier, killing seven people. During that sidewalk ceremony, he blasted the justice system for never pressing charges.

“In this Buenos Aires, which is so vain and proud, we still have slaves,” Bergoglio said. “Everything can be fixed in Buenos Aires with a bribe; we’re bribing our souls, and bribes cover everything.”

Cortez, 37, met Bergoglio at Alameda and asked him to baptize her daughters. He told her to choose the time and place.

“He said the church should go to where it’s needed, instead of the people having to go to the church,” she explained. When Cortez said she would like to hold the ceremony at the foundation’s bottom floor, which doubles as a soup-kitchen, and that the godfather was an atheist and the godmother was Jewish, he didn’t balk.