Cardinal Francis George, the archbishop of Chicago from 1997 to 2014, died Friday at the age of 78 after a long battle with cancer, the Archdiocese of Chicago has confirmed.

George, who retired as Chicago archbishop in the fall of 2014, died Friday morning after a long fight with cancer. George's death was announced by his successor Archbishop Blase Cupich. George announced in December 2014 that doctors had determined their treatment for the cancer found on his kidney had failed.

Appointed to Chicago in 1997 by Pope John Paul II and elevated to the College of Cardinals in 1998, George became a leading figure of his era in many of the most important events in the American church.

He oversaw the contentious new English-language translation of the Roman Missal, one of the biggest changes in Catholic worship in generations. In 2002, at the height of the abuse crisis, he led a group of U.S. bishops who persuaded resistant Vatican officials they should more quickly oust guilty priests -- a policy at the core of reforms meant to restore trust in church leaders.

He was appointed president of the U.S. Conference of Catholic Bishops in 2007, leading the bishops' opposition to ObamaCare, arguing the law would use taxpayer money for funding abortion. In 2012, Catholic Charities of the Archdiocese of Chicago joined dozens of dioceses and Catholic nonprofits in suing the Obama administration over the requirement that employers provide health insurance that covers contraception.

"I don't believe the bishops have been more politically active in recent years, but it is true that our political activity is more adversarial as the law no longer permits the exceptions that used to safeguard believers whose conscience will not permit them to approve of what has become lawful," George told the Jesuit magazine America, in an October 2014 interview.

The first Chicago native to become the city's archbishop, George grew up in a working class neighborhood on Chicago's northwest side. A five-month bout with polio at age 13 left him with a lifelong limp. He was initially rejected from a high school seminary because he was disabled, but went on to become an intellectual leader within the church. George earned two doctorates, spoke Italian, Spanish, French and other languages, and wrote several books. A member of the Missionary Oblates of Mary Immaculate, he eventually helped lead the religious order as vicar general based in Rome. In 1990, he was appointed Bishop of Yakima, Wash., then archbishop of Portland, Ore., before being assigned to Chicago.

George's appointment to the Archdiocese of Chicago, the third-largest diocese in the U.S. with 2.2 million parishioners, underscored the shift under John Paul toward upholding orthodoxy and drawing a more definitive line about what could be considered truly Catholic.

George prioritized upholding doctrine and preserving tradition, earning him the nickname "Francis the Corrector" among some disgruntled priests. George declared liberal Catholicism an "exhausted project," arguing it failed to pass on "the faith in its integrity" on marriage, the priesthood and other issues. "It no longer gives life," George wrote in 2004, in the Catholic magazine Commonweal. He said fighting abortion should be the primary concern of all Catholics.

In September 2014, the pendulum seemed to swing back when Pope Francis appointed Archbishop Blase Cupich as George's successor, who has taken a less confrontational approach on certain social issues. George said he struggled to understand the approach Pope Francis has taken, calling the pontiff's messages "a bit jumbled at times."

"I'm sure he's not confused himself. It's confusing for a lot of people including myself at times. For someone who appreciates clarity, I would like to get a few things clear so I can cooperate," George said in an October 2014 interview with The Chicago Tribune.

As cardinal, George could be blunt when he believed the church was under threat. When a proposed route meant the Chicago Gay Pride Parade would pass a parish around Sunday Mass, George warned the procession could "morph into the Ku Klux Klan, demonstrating in the streets against Catholicism." He later apologized. Addressing what he considered increasing hostility toward Christianity, he said, "I expect to die in bed, my successor will die in prison and his successor will die a martyr in the public square." He later said he was not making a prediction, but describing a worst-case scenario in a commentary that concluded the church would survive despite these travails.

"I don't want to hurt anybody," George told the Tribune. "But if you say, `Unless you agree with me I'll be hurt,' well, that's not a just demand."

Despite his leadership in confronting clergy sex abuse, George faced a 2006 crisis over his own actions, when the Rev. Daniel McCormack, a local priest, was left in a parish for several months despite abuse allegations against him. McCormack eventually pleaded guilty to molesting five children. George apologized for not acting sooner. Thousands of documents released toward the end of George's tenure as part of a settlement with victims revealed the cardinal went against his advisers in one case to delay removing an accused priest, and tried to win early release from a Wisconsin prison for a priest convicted of molesting a child, although the cardinal later reversed his stand to the parole board.

The Associated Press contributed to this report.