A formal Mass to mark the inauguration of Pope Leo XIV will take place on May 18 in St. Peter's Square, the Vatican announced the day after stunning the world with the election of the first pope from the United States in the Church's history.

Leo, formerly Cardinal Robert Francis Prevost , was born in Chicago and has dual Peruvian-American nationality after spending much of his career working there. He attended Villanova University, Catholic Theological Union in Chicago and the Pontifical College of St. Thomas Aquinas in Rome. He was prefect of the Dicastery for Bishops and president of the Pontifical Commission for Latin America. He was named a cardinal less than two years ago.

His selection by the 133 cardinals in the two-day conclave to choose the late Pope Francis ' successor came as a surprise to papal experts and onlookers , who did not expect an American to emerge victorious. He selected the name Leo XIV and greeted a roaring crowd at the Vatican on May 8.

Leo celebrated his first Mass as pontiff at the Vatican's Sistine Chapel on May 9.

"God has .... entrusted this treasure to me so that, with his help, I may be its faithful administrator for the sake of the entire mystical Body of the Church," he said.

The Vatican also announced Leo will hold his first general audience, typically held weekly while the pope is in Rome, on May 21.

Leo has voted in several U.S. elections out of his home state of Illinois, according to records obtained by USA TODAY. He participated in seven separate contests since 2012, including three Republican primaries and last year's hotly contested presidential election.

Many are already speculating on the new pontiff's political allegiances. Before being elected pope, Leo XIV reposted a message on X criticizing President Donald Trump and El Salvador President Nayib Bukele during their Oval Office meeting amid debate about a wrongfully deported man . In February, he posted two op-ed columns critical of Vice President JD Vance , a practicing Catholic, and the administration's stance on immigration.

But while have latched onto the voting records as a sign of the new pontiff's politics, Illinois officials are quick to point out that Prairie State voters are not required to register as members of a political party.

After celebrating his first Mass as pope, Leo XIV is slated to have a full schedule in the coming days. His next engagement is expected to be a May 10 meeting with cardinals. He'll then have midday prayers on May 11 from the balcony of St. Peter's Basilica.

In his first full week as pope, he has a meeting with journalists on May 12 and another with diplomats on May 16. He'll be inaugurated in a Mass on May 18 and have his first general audience on the 21st.

Leo has also inherited religious services, diplomatic meetings and Holy Year events from his predecessor. He'll have to decide whether to carry out a planned trip to Turkey by Francis later in the month, which would include a meeting with Patriarch Bartholomew, the spiritual leader of the Eastern Orthodox Church.

Leo celebrated his first Mass as pope in the Vatican's Sistine Chapel on May 9. The multilingual service began as Leo processed in and sang in Latin along with the Vatican’s Sistine Chapel Choir, one of the oldest and most prestigious in the world.

The first two readings were delivered in English and Spanish. Leo began his homily by addressing the cardinals in English.

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"You have called me to carry the cross and to be blessed with that mission," he said. “And I know I can rely on each and every one of you to walk with me."

Leo delivered the rest of the homily in Italian. He invoked his predecessor saying Pope Francis often taught that Catholics "are called to bear witness to our joyful faith in Christ the Saviour," the Vatican News reported . Leo said this "missionary outreach is desperately needed" in the many places where Christians “are mocked, opposed, despised or at best tolerated and pitied."

World faith leaders embrace Pope Leo XIV

The Dalai Lama, spiritual leader of Tibetan Buddhism, wrote a letter to Pope Leo XIV on May 9 with his greetings to the new pope, his office said.

"I am very happy to have met several of your predecessors and enjoyed friendly conversations with them,” the Dalai Lama wrote. “Over more than four decades, I have also participated in meaningful exchanges with representatives of different religious traditions, my Christian brothers and sisters among them."

“In a period when the world is witnessing so many challenges, your election brings new hope not just to the Catholic community, but to people everywhere who are seeking a happier life in a more compassionate, peaceful world.”

The leaders of the Church of Jesus Christ of Latter-day Saints, commonly known as the Mormon church, also sent a message of welcome to Leo.

"On behalf of the leaders and members of The Church of Jesus Christ of Latter-day Saints, we extend heartfelt prayers and greetings to Pope Leo XIV. This significant moment in time for the Catholic Church is a reminder of the enduring importance of faith to people everywhere," the First Presidency of the church said in a statement. "As fellow followers of Jesus Christ, we look forward to continued opportunities to work together to bless the lives of God’s children everywhere."

More of Leo XIV's roots in the United States are being unearthed, with a New Orleans-based genealogist discovering his maternal grandparents were people of color with Creole ties, according to news reports.

Jari C. Honora, a family historian at the Historic New Orleans Collection, told CNN and the New York Times that Leo's grandparents, Joseph Martinez and Louise (Baquié) Martinez, were identified in genealogical records as people of color. They lived in New Orleans before moving to Chicago, where they had Mildred Martinez, the pope's mother, in 1912.

Both grandparents were listed as Black in a 1900 Census record. Different records list Joseph Martinez's place of birth as Louisiana, Haiti (spelled Hayti in the Census record) and the Dominican Republic, which Honora told the New York Times isn't uncommon in records. He was described as a cigar maker in the Census record.

Honora unearthed the records and posted about them on Facebook, saying he hopes Leo will pay a visit to New Orleans.

"I am truly excited that our city and our Creole community have this wonderful close connection to the Holy Father," Honora said in a post.

John Prevost, the pope's brother, confirmed the ancestry to the Times but said the family does not identify as Black and did not discuss the Creole roots.

“It was never an issue,” John Prevost said.

Pope Leo XIV's father, Louis Marius Prevost, was of French and Italian descent, according to Vatican News. His mother, Mildred Martínez, was of Spanish descent. The Chicago Sun-Times has reported that his father was an educator and his mother a librarian.

He has two brothers, Louis Martín Prevost and John Joseph Prevost.

"We've kind of known he was special, and we used to tease him about being pope when he was 6 years old," Louis Prevost, who lives in Port Charlotte , Florida, told NBC News .

Louis Prevost told NBC affiliate WBBH that when he heard his brother named, “ I just freaked out and said ‘It’s Rob, OMG.’ I was up, dressed, out, just going nuts.”

In an interview with FOX4 , the Pope's sister-in-law, Deborah Prevost, said she and her husband were surprised by the news, and a little saddened that it meant they wouldn't be able to spend as much time with Robert.

John Prevost, who lives in Illinois, told NBC he spoke to his brother just before the conclave to select the new pope began. They played Wordle and Words with Friends together to "keep his mind off life in the real world," John Prevost said.

"I said, 'well are you ready for this?' I said, 'did you watch the movie "Conclave" so you know how to behave?'" And he had just finished watching the movie 'Conclave,' so he knew how to behave," John Prevost told NBC, chuckling.

Chicago brings home the papacy

Chicagoans celebrated the city's native son Pope Leo XIV, not only the first U.S.-born pope but now the pride and joy of the Windy City. He's apparently not a Cubs fan; he's from the South Side and that is squarely in Chicago White Sox territory. But the town doesn't seem to mind.

The Wieners Circle, a famous Chicago hot dog stand, celebrated with a sign which read "CANES NOSTROS IPSE COMEDIT" – Latin for "He has eaten our dogs."

“Everything dope, including the Pope , comes from Chicago!” Mayor Brandon Johnson posted on X. “We hope to welcome you back home soon.”

Chicagoans are fiercely proud of their city's working-class reputation and Pope Leo has a reputation in the Catholic Church for sticking up for worker's rights and the disenfranchised, something highly valued here. Prevost was born in 1955 at Mercy Hospital, about three miles south of the city’s iconic downtown Loop area.

“In this time when Chicago has been demonized, when workers' rights and immigrants' rights have been attacked and people feel in fear, it’s symbolic we have a pope from Chicago, who is actually also a dual citizen. It shows solidarity among countries and workers,” said Alderman Byron Sigcho-Lopez, a South Side city council member. Read more.

Across the nation’s capital, Catholics joyously welcomed the news of the church’s first U.S.-born pope .

“I never thought in my lifetime I would see an American pope,” said Rev. Msgr. W. Ronald Jameson, the director of St. Matthew’s Cathedral. “Today is an extremely joyful day.”

Leo's ascension to the top of the Catholic Church was a surprise, Jameson said, because being a U.S. citizen was long considered a barrier to the papacy.

Economist Lucero Rossi, 36, said Leo was the kind of pope she has been praying for since Francis' death.

“He seems to have a very pro-immigrant agenda,” she said, “so I am very happy about that.”

Rossi watched as he made his first public appearance at St. Peter’s Basilica, opening in Italian with “Peace be with you all.” But what stuck out most of all was the moment he greeted his diocese in Chicago and Peru in Spanish – not English.

“I really loved that,” said Rossi, born in Mexico. “That was an embrace of the Latin American world.”

Leo XIV speaks English, Spanish, French, Italian and Portuguese, and can read Latin and German, according to the National Catholic Reporter .

After he was announced the new pope, Leo addressed a massive crowd at St. Peter's Square on May 8 in Spanish and Italian, but not English. He delivered his first Mass the next day in English, Spanish and Italian.

Popes aren’t required to choose a new name, according to the National Catholic Register. But for those that do, the new moniker is a symbol of their new stage in life , their entry into a new community and their new way of serving God and other people.

A new pope may take the name of a predecessor or saint “out of respect, admiration, or recognition,” the Vatican News reported. Some names, like Leo, have been used more than a dozen times while others, like Peter, have been used only once. Taking a unique papal name may signal forthcoming changes in church doctrine.

Leo was born in Chicago as Robert Francis Prevost and went on to attend the now-closed St. Augustine Catholic Seminary, a boarding school in west Michigan for boys in grades 9-12, the Detroit Free Press, part of the USA TODAY Network, reported.

Is Pope Leo XIV, a Chicago native, a Cubs or White Sox fan ?

The pope hails from the South Side of the city − White Sox territory − but the Cubs are a major brand that easily could have swooped him up. There have been some reports of which side Leo leans, but a family member has given sports fans the answer they've been seeking.

According to his brother, Pope Leo is loyal to the South Side. John Prevost revealed his brother is a White Sox fan in an interview with WGN TV .

“He was never, ever a Cubs fan. So I don’t know where that came from. He was always a Sox fan,” John Prevost said.

His mother was a Cubs fan and his father was a fan of the St. Louis Cardinals , John Prevost said.