A priest of Mainz, the new prefect spent most of his priesthood as a theology professor in Munich before his appointment to Regensburg in 1992. He has served as a member of the congregation since 2002.
Given common perceptions of the current pontificate, it's worth noting that Müller's appointment to lead the CDF survived an attempted subterfuge by some conservatives in Vatican circles, who — among other things — sought to play up a longstanding friendship the new "Grand Inqusitor" has kept with a leading architect of liberation theology, the Peruvian Dominican Gustavo Gutierrez.
Among CDF's relatively new areas of jurisdiction are several matters of sizable import to the church in the English-speaking world, above all deciding final outcomes to the worldwide church's clergy sex-abuse cases (a task entrusted to Ratzinger in 2001 after a Curial turf-fight), and the implementation of Anglicanorum coetibus, the Pope's 2009 initiative allowing for Anglican groups to enter the Catholic church as collective units, with their own liturgy and governing structures. In the space of just over a year, the latter development has arguably made for the Western church's largest boon of married priests in the millennium since mandatory celibacy became universal policy.
In 2006, Müller acted to halt over 2 million Euros in Church funding to pro-abortion ‘Catholic’ groups after their dissident activities were exposed by faithful Catholic bloggers and a group called Union for the Associations Faithful to the Pope.
Central Committee of German Catholics had received more than two million Euros in financing from the Church prior to the cut off.
The association Donum Vitae created by the Committee came under fire for aiding women in obtaining abortions. The association fulfilled pre-abortion requirements for women by offering counseling and certificates, clearing the way for the abortion procedure. Moreover, the Committee openly criticized the hierarchy of the Church, calling for the development of a democratic structure that would give authority to the laity.
Archbishop Müller also suppressed the Diocesan council of Lay People and thirty-three other dissident organizations.
Some people have expressed misgivings over Müller’s open thoughts on a range of theological questions, including Liberation Theology. Let us not forget that Joseph Ratzinger used a point from Liberation Theology as a starting point for a book on liturgical worship: Christ is the Liberator who frees us from sin and death and liturgical worship is as an act of the Liberator, liberating for those who participate. Frankly, I think that focusing on the fact that Müller has read Liberation Theology is not very productive. Liberation Theology has been pretty much junked, and picked over for the good points it had.
Note also that Müller begins his tenure as Prefect on the eve of the Year of Faith, which is clearly an important project for Benedict. The Holy Father must see in Müller, as Prefect of “Faith”, someone who can advance that project.
Regarding the SSPX, the Holy Father made Archbp. DiNoia the Vice-President of the Pontifical Commission “Ecclesia Dei“. I imagine he will exert greater immediate influence. Nevertheless, Müller will have a different view of the stand off than did the previous Prefect.
Müller has made some statements about clerical celibacy and Mariology that have a few people scratching their heads. That said, his job is to make this run smoothly at the Congregation, not to shape the Church’s doctrine.
UPDATE III: John Allen Jr.'s take on the appointment. (The comments section is interesting. Reaction on the Liberal side is as negative as that from the traditionalist side. Maybe it means the Holy Father has struck the right balance?)
The pope’s new doctrinal czar has a profile in Germany as a staunch defender of Catholic orthodoxy, yet not an ideologue. Among other things, Müller has a strong friendship with Peruvian liberation theologian Gustavo Guttierez.
Müller clearly enjoys the pope’s confidence.
Aside from the fact that Müller is the bishop of the pope’s home diocese, where Benedict’s brother Geörg still resides, he’s also the editor of Benedict’s “Opera Omnia,” a comprehensive collection of all the pope’s theological writings. Müller himself is a prolific author, having written more than 400 works on a wide variety of theological topics.
Despite his broadly conservative reputation, Müller actually earned his doctorate in 1977 under then-Fr. Karl Lehmann, who went on to become the cardinal of Mainz and the leader of the moderate wing of the German bishops’ conference. Müller’s dissertation was on the famed German Protestant theologian Dietrich Bonhoeffer.
Moreover, Müller is also a close personal friend of Guttierez, widely seen as the father of the liberation theology movement in Latin America. Every year since 1998, Müller has travelled to Peru to take a course from Guttierez, and has spent time living with farmers in a rural parish near the border with Bolivia.
Müller has been rumored to be in pole position to take over at the doctrinal congregation for some time, and late last year there was a push in traditionalist circles to try to block the appointment. E-mails were circulated suggesting that Müller, already a member of the Congregation for the Doctrine of the Faith, is not a man of “secure doctrine.”
Specifically, the e-mails cited Müller for espousing suspect positions on the virginity of Mary (which he said in a 2003 book shouldn’t be understood in a “physiological” sense), the Eucharist (Müller has apparently counseled against using the term “body and blood of Christ” to describe the consecrated bread and wine at Mass), and ecumenism (last October, Müller declared that Protestants are “already part of the church” founded by Christ.)
Defenders of Müller argued that in each case, his words had either been taken out of context or were consistent with official teaching.