Considered the guiding light on doctrinal issues during Pope John Paul II's pontificate, Pope Benedict XVI entered this week's conclave as German Cardinal Joseph Ratzinger, one of the most respected, influential and controversial members of the College of Cardinals.

Since 1981 the 78-year-old pontiff --- regarded as one of the church's sharpest theologians --- headed the Congregation for the Doctrine of the Faith, the Vatican department charged with defending orthodoxy in virtually every area of church life.

Since November 2002 he has been dean of the College of Cardinals, a key position in the time between popes. As such, he presided over the pre-conclave meetings of cardinals in Rome, set agendas for discussion and action, and was responsible for a number of procedural decisions during the conclave.

Over the years, Pope Benedict met quietly once a week with the pope to discuss doctrinal and other major issues facing the church. Insiders say his influence was second to none when it came to setting church priorities and directions and responding to moral and doctrinal challenges.

"I'm not the Grand Inquisitor," Pope Benedict once said in an interview. But to the outside world, he has been known as the Vatican's enforcer. He made the biggest headlines when his congregation silenced or excommunicated theologians, withdrew church approval of certain books, helped rewrite liturgical translations, set boundaries on ecumenical dialogues, took over the handling of clergy sex abuse cases against minors, curbed the role of bishops' conferences and pressured religious orders to suspend wayward members.

In 2003, the doctrinal congregation issued an important document that said Catholic politicians must not ignore essential church teachings, particularly on human life. That set the stage for a long debate during the 2004 U.S. election campaign on whether Democratic Sen. John F. Kerry, a Catholic who supports legalized abortion, should be given Communion.

Pope Benedict's congregation also published a document asking Catholic lawmakers to fight a growing movement to legalize same-sex marriage.

White-haired and soft-spoken, Pope Benedict comes across in person as a thoughtful and precise intellectual with a dry sense of humor. A frequent participant at Vatican press conferences, he is a familiar figure to the international group of reporters who cover the church.

He is also well-known by the church hierarchy around the world, and his speeches at cardinal consistories, synods of bishops and other assemblies often have the weight of a keynote address. When Pope Benedict talks, people listen.

Sometimes his remarks have been bluntly critical, on such diverse topics as dissident theologians, liberation theology, "abuses" in lay ministry, homosexuality, women as priests, feminism among nuns, premarital sex, abortion, liturgical reform and rock music.

As Pope John Paul's pontificate developed, some Vatican observers said the cardinal's influence grew.

"He's become the last check on everything, the final word on orthodoxy. Everything is passed through his congregation," one Vatican official said in 1998.

In his first decade at the helm of the doctrinal congregation, Pope Benedict zeroed in on liberation theology as the most urgent challenge to the faith. He silenced Latin American theologians like Franciscan Father Leonardo Boff and guided the preparation of two Vatican documents that condemned the use of Marxist political concepts in Catholic theology.

But after the collapse of Marxism as a global ideology, Pope Benedict identified a new, central threat to the faith: relativism. He said relativism is an especially difficult problem for the church because its main ideas --- compromise and a rejection of absolute positions --- are so deeply imbedded in democratic society.

More and more, he has warned, anything religious is considered "subjective." As a result, he said, in places like his native Germany, the issue of abortion is being confronted with "political correctness" instead of moral judgment.

He said modern theologians are among those who have mistakenly applied relativistic concepts to religion and ethics. He said Jesus is widely seen today as "one religious leader among others," concepts like dogma are viewed as too inflexible and the church is accused of intransigence.

Pope Benedict has been particularly sensitive to wayward trends in Asian theology, especially as they find popular expression. He banned the best-selling books of a late Jesuit theologian from India and declared a Sri Lankan theologian excommunicated for his writings on Mary and the faith.

After review by Pope Benedict's congregation, U.S. Father Charles Curran, who questioned church teaching against artificial birth control, was removed from his teaching position at The Catholic University of America in 1987. In 2005, Pope Benedict made a similar judgment on a book touching on the divinity and salvific mediation of Jesus by Jesuit Father Roger Haight, who was banned from teaching Catholic theology.

Pope Benedict also has focused on ordinary Catholics, saying there can be no compromise on dissent by lay faithful. The cardinal helped prepare a papal instruction on the subject in 1998 and accompanied it with his own commentary warning Catholics they would put themselves outside the communion of the church if they reject its teachings on eight specific issues.

The same year, he issued a document on papal primacy --- a topic of intense ecumenical discussion --- saying that, as a matter of faith, only the pope has the authority to make changes in his universal ministry.

Pope Benedict's theological ideas are based on years of study, pastoral ministry and Vatican experience. Born in Marktl am Inn April 16, 1927, the son of a rural policeman, his family moved several times during his younger years. His priestly studies began early but were interrupted by World War II.

In a book of memoirs, Pope Benedict recalled that while a seminarian, he was enrolled by school officials in the Hitler Youth program; he soon stopped going to meetings. After being drafted in 1943 he served for a year on an anti-aircraft unit that tracked Allied bombardments. At the end of the war he spent time in a U.S. prisoner-of-war camp before being released.

Ordained in 1951, he received a doctorate and a licentiate in theology from the University of Munich, where he studied until 1957. He taught dogma and fundamental theology at the University of Freising in 1958-59, then lectured at the University of Bonn from 1959-1969, at Munster from 1963-66 and at Tubingen from 1966-69. In 1969 he was appointed professor of dogma and of the history of dogmas at the University of Regensburg, where he also served as vice president until 1977.

A theological consultant to West German Cardinal Joseph Frings, he came to the Second Vatican Council as an expert or "peritus." At the council, he was said to have played an influential role in discussions among the German-speaking participants and gained a reputation as a progressive theologian.

After the council, he published several major books, including "Introduction to Christianity," "Dogma and Revelation" and "Eschatology." He was named a member of the International Theological Commission in 1969.

Pope Paul VI appointed him archbishop of Munich and Freising in 1977 and named him a cardinal the following year.

Pope Benedict has frequently criticized the growth of church bureaucracy and its output of studies, reports and meetings. Asked once whether the Vatican would operate better in Germany, he responded, "What a disaster! The church would be too organized.

"The saints were people of creativity," he added, "not bureaucratic functionaries."

Until April 19, Pope Benedict lived in an apartment just outside the Vatican's St. Anne's Gate. He walked to work daily across St. Peter's Square, rarely attracting people's notice.

---CNS