VATICAN CITY (AP) — Pope Leo XIV was set to declare a 15-year-old computer whiz, Carlo Acutis, the first millennial saint on Sunday, giving the next generation of Catholics a relatable role model who used technology to spread the faith and earn the nickname "God's influencer."

An open-air Mass in St. Peter's Square, the first saint-making ceremony of Leo's pontificate, was expected to draw hundreds of thousands of people and was also set to canonize another popular Italian figure who died young, Pier Giorgio Frassati.

Both ceremonies were scheduled for earlier this year, but were postponed following Pope Francis' death in April. Francis had fervently pushed the Acutis sainthood case forward, convinced that the church needed someone like him to attract young Catholics to the faith while addressing the promises and perils of the digital age.

Like Francis before him, Leo has expressed concern about the risks of technology, particularly artificial intelligence, and about online relationships replacing human ones.

Acutis was born on May 3, 1991, in London to a wealthy but not particularly observant Catholic family. They moved back to Milan soon after he was born and he enjoyed a typical, happy childhood, albeit marked by increasingly intense religious devotion.

Acutis was particularly interested in computer science and devoured college-level books on programming even as a youngster. He earned the nickname "God's Influencer," thanks to his main tech legacy: a multilingual website documenting so-called Eucharistic miracles recognized by the church, a project he completed at a time when the development of such sites was the domain of professionals.

Acutis was known to spend hours in prayer before the Eucharist each day. The Catholic hierarchy has been trying to promote the practice of Eucharistic adoration because, according to polls, most Catholics don't believe Christ is physically present in the Eucharistic hosts.

In October 2006, at age 15, Acutis fell ill with what was quickly diagnosed as acute leukemia. Within days, he was dead. He was entombed in Assisi, which known for its association with another popular saint, St. Francis.

In the years since his death, young Catholics have flocked by the millions to Assisi, where they can see the young Acutis through a glass-sided tomb, dressed in jeans, Nike sneakers and a sweatshirt.

Acutis has proven enormously popular with young Catholics, who see in him a relatable, modern day role model.

"It's like I can maybe not be as great as Carlo may be, but I can be looking after him and be like, 'What would Carlo do?'" said Leo Kowalsky, an 8th grader at a Chicago school attached to the Blessed Carlo Acutis Parish.

Kowalsky said he was particularly excited that his own namesake — Pope Leo — would be canonizing the patron of his school. "It's kind of all mashed up into one thing, so it is a joy to be a part of," Kowalsky said in an interview last week.

Frassati, the other saint being canonized Sunday, lived from 1901-1925, when he died at age 24 of polio. He was born into a prominent Turin family but is known for his devotion to serving the poor and carrying out acts of charity while spreading his faith to his friends.