Fr. Richard McBrien, who as a scholar brought distinction to a university theology department and who as an author and often-interviewed popular expert explained the Catholic church to the wider world, died early Sunday morning. He was 78.

McBrien had been seriously ill for several years and had moved recently from South Bend, Ind., to his native Connecticut.

It would be difficult to find a figure comparable in making understandable to a broad public the basic beliefs and traditions of the Roman Catholic church.

For more than three decades, he was the star of the theology faculty at the University of Notre Dame and the go-to voice on all matters Catholic in the popular press. His books, particularly Catholicism, Lives of the Popes and Lives of the Saints, were staples of libraries, Catholic and non-Catholic alike.

At his peak in the 1980s and '90s, it is arguable that McBrien had a higher media profile than anyone in the Catholic church other than Pope John Paul II. He was the ideal interview: knowledgeable, able to express complex ideas in digestible sound bites, and utterly unafraid of controversy.

"I don't hold things back," McBrien said in a 1990 profile by the Chicago Tribune, adding in a rare moment of understatement: "I'm outspoken."

Unabashedly on the progressive side of most Catholic debates, McBrien advocated the ordination of women priests, an end to mandatory celibacy for priests, moral approval of artificial birth control, and decentralization of power in the church. In so doing, he helped to define the battle lines within Catholicism over the legacy of the Second Vatican Council (1962-65).

He was a former president of the Catholic Theological Society of America and former chair of the theology department at the University of Notre Dame. To fans both inside and outside the theological guild, McBrien was a double icon. He lifted the status of Catholic theology, and American Catholic theology in particular, by his media visibility and literary accomplishment. He also cheered the liberal wing of the church by lending intellectual heft to its reading of Vatican II.

"No Catholic theologian in the United States has made a larger contribution to the reception of Vatican II than Richard P. McBrien," said theologian Fr. Charles E. Curran, Elizabeth Scurlock University Professor of Human Values at Southern Methodist University in Dallas.

St. Joseph Sr. Elizabeth Johnson, professor of theology at Fordham University in New York, echoed that view. Both Curran and Johnson spoke in conjunction with a 2012 Notre Dame ceremony honoring McBrien for 30 years of service.

"His love of the church and his knowledge of its history, both sinful and graced, led a whole generation to a greater critical appreciation of what it means to be Catholic," Johnson said. "His insights have pierced the fog of pretense and at times outright deception to bring a modicum of transparency to the exercise of power."

Notre Dame President Holy Cross Fr. John I. Jenkins called McBrien "a leading theologian and commentator on the Catholic church” in a statement released Jan. 26. “While often controversial, his work came from a deep love of and hope for the Church. We pray for eternal rest for his soul,” Jenkins said.

For supporters of the conservative direction set by Popes John Paul II and Benedict XVI, McBrien was instead a favorite bête noire. Foes routinely tried to get him fired at Notre Dame, occasionally tried to cajole bishops into excommunicating him, pressured diocesan papers to drop his syndicated column, and once even lodged charges of plagiarism. University officials investigated the plagiarism complaint in 2006, and McBrien was cleared.

McBrien's critics didn't just circulate in the blogosphere or on op-ed pages. At times, they were right down the hall at Notre Dame.

"McBrien has terrible ideas," Ralph McInerny bluntly said in 1990. The late McInerny was a renowned philosopher and author of the "Father Dowling" mystery series, as well as a stern critic of what he once called the "pell-mell pursuit of warm and fuzzy Catholicism" he associated with McBrien.

"I think the demonology he works with is that once we had a hierarchical view of the church, which was authoritarian," McInerny said. "Then we had Vatican II and, he believes, that model was thrown out. His view is wrong."

It might be said that McBrien was genetically destined never to back down from a fight, as the son of an Irish cop and an Italian nurse who grew up in West Hartford, Conn. Born in 1936, he was the fourth of five children. He imbibed a deep sense of Catholic identity from the cocoon of pre-Vatican II American Catholicism.

"I loved it and was nurtured and shaped by it," McBrien once said. "I had no regrets. I'm not angry about it. There were also a lot of progressive currents in the church before Vatican II, and I came into contact with them in my parish and in my seminary."

McBrien earned his bachelor's degree at St. Thomas Seminary in Bloomfield, Conn., in 1956, and a master's at St. John Seminary in Brighton, Mass., in 1962. That same year, he was ordained a priest of the Hartford, Conn., archdiocese. He studied for his doctorate in theology at Rome's Jesuit-run Gregorian University during the Vatican II years and returned to the United States in 1965.

From the close of the council onward, McBrien became perhaps its leading English-language interpreter from his perch at a series of America's most prestigious Catholic venues.

From 1965 to 1970, McBrien served as professor of theology and dean of studies at the Pope John XXIII National Seminary in Weston, Mass. From 1970 to 1980, he was a professor of theology at Boston College as well as director of its Institute of Religious Education and Pastoral Ministry. Reflecting his growing impact outside his own discipline, McBrien was chosen as the first visiting fellow in the John Fitzgerald Kennedy School of Government at Harvard University in 1975-76.

McBrien's early titles reflected his penchant for popularization, including Do We Need the Church? (Harper and Row, 1969) and The Remaking of the Church: An Agenda for Reform (Harper and Row, 1973). The latter carried an introduction by Belgian Cardinal Leo Joseph Suenens, considered among the architects of Vatican II.

McBrien also began writing a column on Catholic affairs in 1966, which he would continue to churn out on a weekly basis for more than four decades. Aside from frequent guest opinion pieces for outlets such as The New York Times and The New Republic, McBrien was also a regular columnist for the National Catholic Reporter.

Early on, McBrien's work brought acclaim. He was elected president of the Catholic Theological Society of America in 1972-74, and won its John Courtney Murray Award "for outstanding and distinguished achievement in theology" in 1976.

Notre Dame's iconic president Holy Cross Fr. Theodore Hesburgh recruited McBrien to South Bend in 1980, partly for what his critics would come to regard as a grand irony — to beef up the Catholic character of the theology department.

Hesburgh said at the time he was concerned that the ecumenical and interfaith enthusiasm after Vatican II had played down the specifically Catholic dimension of the department, and felt McBrien's command of the tradition would bring greater Catholic depth as opposed to a vague "religious studies" orientation.

McBrien served as chair of Notre Dame's theology department from 1980 to 1991.

In the same year he moved to South Bend, McBrien also published what would become his most celebrated, and most controversial, book: Catholicism, styled as a synthesis of Catholic theology, history and moral values, and intended for the general reader. (McBrien wrote that to understand the book, a reader needed only two prerequisites: "intelligence and a basic interest in Catholicism.")

The original version of Catholicism came out in two volumes and ran to almost 1,300 pages, though McBrien also published a one-volume study edition in 1981. It became a mass-market triumph, selling more than 150,000 copies worldwide. McBrien brought out a revised and updated edition in 1994. The approach was to present core teachings and practices along with a range of opinions about them, inviting readers to reach their own conclusions.

The influence of John Paul II and the increasingly conservative nature of his episcopal appointments, especially in the United States, began to have a chilling effect on theologians and what they published.

In addition to celebrity, Catholicism brought McBrien controversy. In 1985, the Committee on Doctrine of the U.S. bishops' conference objected that the book's "presentation is not supportive of the church's authoritative teaching" on certain matters, especially contraception and the ordination of women.

When McBrien brought out the revised edition of Catholicism a decade later, the bishops expanded their criticism, complaining of "an overemphasis on the plurality of opinion within the Catholic theological tradition that makes it difficult at times for the reader to discern the normative core of that tradition." The bishops faulted McBrien's treatment of Jesus and sin, the virgin birth, Mary's perpetual virginity, the fatherhood of God, and papal infallibility, as well as contraception and women priests.

The bishops discouraged the use of Catholicism in undergraduate theology courses and in parish formation programs. The cumulative effect was to make attitudes toward McBrien's book a placeholder for broader tensions in the church.

"In pre-Vatican II seminaries, students often studied theological 'manuals,' which summarized Catholic theology," Jesuit Fr. Tom Reese said. "Today, the Catechism of the Catholic Church provides that function for conservative seminarians, while McBrien's Catholicism is the source for others."

McBrien's friend and colleague Eugene Cullen Kennedy wrote in 2006 that the owner of a Catholic bookstore actually called security to toss him out when Kennedy persisted in asking why it didn't carry Catholicism.

Despite being a lightning rod, McBrien was never subject to any ecclesiastical censure and always remained a priest in good standing.

"I'm not easily disposed of, even though some people would like to have had that done," McBrien laughingly said in a 2008 interview.

McBrien's command of the Catholic tradition was also on display in 1995, when he served as general editor of the HarperCollins Encyclopedia of Catholicism. He went on to produce two other resources that even his most ferocious critics now regard as indispensable: Lives of the Popes in 1997 and Lives of the Saints in 2001. In total, he authored 25 books in addition to hundreds of articles, scholarly essays and lectures.

At the height of McBrien's influence, almost 25 diocesan papers and a couple dozen parish bulletins carried his column. As the papacies of John Paul II and Benedict XVI wore on, McBrien found it increasingly difficult to penetrate official venues. By the end, only six diocesan papers carried the column.

In effect, McBrien became the voice of Catholicism's loyal opposition, once predicting that today's turn to tradition will be only "a temporary pause in the forward movement of the Catholic church that began with John XXIII and Vatican II."

"I think it would be wrong to clam up and let [people] think the church has been completely taken over by a group that wants everyone to march in step," McBrien said in 1990. "I want to speak for those who don't want to march with this crowd. I'm saying you don't have to make that choice. You don't have to obey or get out. That summarizes my ministry."

Even McBrien's critics recognize the significance of his passing.

"Fr. McBrien was an able and indefatigable proponent of the Catholic revolution that never was and, now, never will be," said George Weigel, widely seen as America's leading conservative Catholic commentator.

"We shared the op-ed pages of many Catholic newspapers for years, and I'll miss the sparring partner who was always gracious in our personal contacts," Weigel said. "His death is another marker of the end of an era in U.S. Catholic history."

For McBrien's admirers, he remains a leading symbol of roads waiting to be taken.

"It is scandalous that, in a problem-filled church, McBrien is considered a question when he is really one of the answers," Kennedy wrote in 2006*, expressing a sentiment that McBrien's wide following would doubtless echo today.

*An earlier version of this story listed the incorrect year.