As the butler to Pope Benedict XVI, Paolo Gabriele lived in a Vatican City apartment just inside the walls of the world’s smallest country. He rose before 7 most mornings, walked four minutes to the papal apartments in the Apostolic Palace, and laid out the red papal shoes and white dress clothes for the Holy Father.

Mr. Gabriele often joined Benedict in prayer at a private morning Mass. He poured his coffee, held the pope’s umbrella in the rain and rode shotgun in the popemobile. And in 2010, he reportedly began photocopying papal letters and memos, believing that his beloved boss, the leader of the Catholic Church, was being misinformed by his advisers.

Convinced that “evil and corruption” had overtaken the Holy See, he took hundreds of secret papal documents to an Italian journalist, setting off a 2012 scandal known as Vatileaks. The documents revealed allegations of corruption and negligence, punctured the Vatican’s reputation as one of the world’s most impenetrable institutions, and were later seen as influencing Benedict’s landmark decision to step down.

Mr. Gabriele was convicted of stealing the documents by a Vatican court and served two months in jail before being pardoned by Benedict and exiled from Vatican City, his professional home for nearly two decades. He worked at a children’s hospital in Rome, administered by the Holy See, before dying Nov. 24 at age 54.

His death was announced by the Vatican’s media service, Vatican News, which cited a long illness but did not offer further details. The director of the Vatican press office, Matteo Bruni, did not immediately respond to requests for information.

Mr. Gabriele’s leaks exposed Vatican infighting, including criticism of the powerful Cardinal Tarcisio Bertone; clashes over the management of the Vatican bank, whose president was ousted amid debates over financial transparency; and allegations that the Holy See had awarded excessive contracts to cronies for construction work.

But the disclosures were perhaps just as significant for marking a dramatic breach of security, representing what critics described as a betrayal from one of the pope’s closest aides. After months in which secret documents were mysteriously leaked to the Italian media, Mr. Gabriele’s conviction spurred shocked headlines: Indeed, “the butler did it.”

The Vatican faced further leaking scandals in recent years under Benedict’s successor, Pope Francis, who ascended to the papacy after Benedict resigned in February 2013, the first pope in nearly six centuries to do so. He was 85 and cited failing strength of “mind and body” but had also faced a wave of challenges that included Vatileaks, financial troubles at the Holy See and criticism over the church’s handling of sexual abuse cases.

As Benedict’s butler, Mr. Gabriele said, he was “the layman closest to the Holy Father.” Raised in a working-class district in Rome, he studied painting at a fine-arts high school, sprinkled his conversations with quotes from Scripture and supported himself in part by scrubbing toilets at a Catholic church, according to a 2013 profile in GQ.

His rise through the Vatican was reportedly fueled by an admiring cardinal — or perhaps a bishop — who asked, “Who cleaned this bathroom?,” leading Mr. Gabriele on a journey from Vatican toilet cleaner to marble polisher to papal butler. (Italian media outlets would later offer competing reports accounting for his career, suggesting that he had been recruited to the Holy See by an influential lay movement or sponsored by an Argentine cardinal.)

After Pope John Paul II died in 2005, leading to Benedict’s election, the longtime valet Angelo Gugel announced his retirement, following nearly three decades of service to three popes. Mr. Gabriele succeeded him in 2006 and moved into a Vatican apartment with his wife, Manuela Citti, and three children, who survive him.

“His black gelled hair, dark suits and fleshy cheeks clenched in a cherubic grimace became so familiar around the Vatican Gardens that clerics affectionately called him Paoletto,” journalist Jason Horowitz wrote in a 2013 Washington Post report.

Mr. Gabriele shared an office with the pope’s personal secretary, giving him access to documents that included letters from Carlo Maria Viganò, an archbishop who was transferred from his Vatican posting after trying to fight “corruption and abuse,” as he wrote, and who suggested the pope had been “kept in the dark” about his efforts.

Reading the letters, Mr. Gabriele was spurred to take action. “Seeing evil and corruption everywhere in the Church,” he later told Vatican investigators, “I was sure that a shock, even in the media, might be just the thing to bring the Church back on the right track.” He was not a thief, he insisted, but had “acted only out of visceral love for the church of Christ and for its visible head on Earth.”

According to news reports, he reached out to Italian journalist Gianluigi Nuzzi through intermediaries who assessed the reporter’s trustworthiness. In 2011, they brought Nuzzi to a Rome apartment where Mr. Gabriele identified himself using a code name, “Maria,” after Jesus’ mother. He soon began turning over papal files, meeting Nuzzi with pages taped to his back or stored in a computer thumb drive sewn into his necktie.

Many of the files were published in Nuzzi’s May 2012 book, “His Holiness: The Secret Papers of Benedict XVI,” which spurred a leak investigation at the Holy See. Mr. Gabriele said he “went to a confessor” and then turned himself in, prompting Vatican investigators to find some 1,000 papal documents in his apartment.

In court, he described himself as an “agent” of the Holy Spirit and testified that he loved the pope “as a son loves his father.” He was sometimes cut off at the trial, forbidden from discussing his conversations with various cardinals, and was portrayed by Vatican officials as a lone, misguided operator.

News reports suggested he may have acted with about 20 others. A Vatican computer expert, Claudio Sciarpelletti, was later convicted of obstruction of justice in the case and given a two-month suspended sentence before being pardoned.

A Vatican tribunal convicted Mr. Gabriele of aggravated theft in October 2012 and sentenced him to 18 months in the Gendarmerie barracks. He passed the time by painting and was pardoned by Benedict three days before Christmas, following a 15-minute jailhouse meeting.

Banished from Vatican City, he was given a new home and a job, in what the Vatican described as a “paternal gesture.” By then, the Vatican had also named a new papal butler while reportedly making some changes to office protocol, eliminating the butler’s desk space next to Benedict’s personal secretary. It was there, in full view of others, that Mr. Gabriele said he had photocopied documents during office hours.

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