The Holy Father has named as Capo Ufficio [Head of the Office, or Office Manager] of the Congregation for Divine Worship and Discipline of the Sacraments Reverend Father Abbot Dom Michael John Zielinski, OSB Oliv.
Thus the announcement on the Vatican website today.
The Capo Ufficio is below the number 3 of a congregation, ranking below the Prefect, Secretary, and Undersecretary. The prefect is Cardinal Antonio Cañizares Llovera, the Secretary is Archbishop Arthur Roche, and the Undersecretary is Msgr. Tony Ward, SM. Ward is usually credited as the author of Liturgiam Authenticam and a co-author of Redemptionis Sacramentum.
Abbot Zielinski has been the Vice President of the Pontifical Commission for the Cultural Heritage of the Church, and Vice President of the Pontifical Commission for Sacred Archaeology. He was named a consultor to the Congregation two years ago this month, as reported earlier on Pray Tell along with some other familiar names of a similar persuasion.
A flavor of his views can be gained from a recent paper on the Culture and Heritage of the Classical Roman Rite.
A websearch also reveals that he presided at a Pontifical High Mass in the EF in April 2009 at the London Oratory. A selection of other brief writings and oral responses can be found at the Vatican website, Catholic News Agency, and New Liturgical Movement to name only a few.