An Italian teenager who died of leukemia in 2006 at the age of 15 was on Sunday proclaimed a saint of the Catholic Church, becoming the first millennial to be canonized.

London-born Carlo Acutis, dubbed "God's influencer" due to his use of the internet and social media to spread the faith during his short lifetime, was canonized by Pope Leo XIV in a ceremony in St Peter's Square attended by tens of thousands of people, including his family.

Pier Giorgio Frassati, a young Italian mountaineering enthusiast who passed away from polio in 1925, aged 24, was also made a saint.

"Saints Pier Giorgio Frassati and Carlo Acutis are an invitation to all of us, especially young people, not to squander our lives, but to direct them upwards and make them masterpieces," Pope Leo said in his homily, in front of tapestries displayed on the facade of St. Peter's Basilica showing images of both young men.

"Even when illness struck them and cut short their young lives, not even this stopped them nor prevented them from loving, offering themselves to God," he said.

'Cyber-apostle' Acutis

Acutis, who was born in London in 1991 to Italian parents, grew up in Milan in northern Italy.

Despite his family not being particularly religious, the young man became a devout Catholic, attending mass daily and developing a reputation for kindness, standing up for bullied children and bringing food and sleeping bags to homeless people.

But other aspects of his life were less traditional. A keen gamer, Acutis taught himself basic coding and used his skills to document miracles and other elements of the Catholic faith online.

The body of the so-called "cyber-apostle," dressed in modern jeans and a pair of Nike trainers, lies preserved in a glass tomb in the central Italian town of Assisi, which was visited by over one million pilgrims last year alone.

Acutis: a millennial saint for young people

Acutis had a particular impact on young Catholics, many of whom were present at his canonization ceremony at the Vatican. "I'm happy to see so many young people!" said Pope Leo ahead of the mass.

"He was able to combine his everyday life — school, football and his passion for IT and computers — with an unshakeable faith," 17-year-old Filippo Bellaviti told the AFP news agency.

"Seeing people from so many parts of the world, you can see the affection for Carlo for what he's done."

Eleanor Hauser, 15, on a school trip to Italy from the state of North Carolina in the United States, said she had been told about Acutis by her Catholic grandmother.

"It shows that you can do so much even when you're young, you can make an impact on the world no matter how old you are," she said.

How does one become a saint?

Being made a saint is the result of a long and meticulous process, involving an investigation by Vatican specialists who assess whether the obligatory two miracles have taken place.

Miracles attributed to Acutis include the healing of a Brazilian child suffering from a rare pancreatic malformation, and the recovery of a Costa Rican student seriously injured in a traffic accident.

Acutis' mother, Antonia Salzano, said her son was proof that "we are all called to be saints ... everyone is special."

Edited by: Saim Dušan Inayatullah