In a major shake-up of the Vatican's administration, Pope Francis has ousted the head of the Catholic Church office that handles sex abuse cases.
The move follows the high-profile exit of fellow conservative Cardinal George Pell, who last week took a leave of absence to return to Australia to face historical sexual abuse charges.
A brief Vatican statement said Cardinal Gerhard Ludwig Mueller's five-year mandate as head of the Congregation for the Doctrine of the Faith, a department charged with defending Catholic doctrine, would not be renewed.
The position is the most important one that a pope fills in the Vatican hierarchy after the Secretary of State.
Most incumbents keep it until they retire, which in Cardinal Mueller's case would have been in six years.
The 69-year-old cardinal, who was appointed by Pope Benedict in 2012, will be succeeded by the department's number two, Archbishop Luis Francisco Ladaria Ferrer.
Archbishop Ladaria, a 73-year-old Spaniard who, like the Argentine pope is a member of the Jesuit order, is said by those who know him to be a soft-spoken person who shuns the limelight — Cardinal Mueller, by contrast, often appears in the media.
"They speak the same language and Ladaria is someone who is meek. He does not agitate the Pope and does not threaten him," a priest who works in the Vatican and knows both Cardinal Mueller and Archbishop Ladaria told Reuters, asking not to be named.
Since his election in 2013, Pope Francis has given hope to progressives who want him to forge ahead with his vision for a more welcoming church that concentrates on mercy rather than the strict enforcement of rigid rules they see as antiquated.
Conflicts over divorce, remarriage
Cardinal Mueller is one of several cardinals in the Vatican who have publicly sparred with the Pope.
In 2015, both Cardinal Mueller and Cardinal Pell were among 13 cardinals who signed a secret letter to the Pope complaining that a meeting of bishops discussing family issues was stacked in favour of liberals.
The letter was leaked, embarrassing the signatories.
Cardinal Mueller has criticised parts of a 2016 papal treatise called "Amoris Laetitia" (The Joy of Love), a cornerstone document of Pope Francis' attempt to make the 1.2-billion-member church more inclusive and less condemning.
Conservatives have concentrated their criticism on the document's opening to Catholics who divorce and remarry in civil ceremonies, without getting church annulments.
Under church law they cannot receive communion unless they abstain from sex with their new partner, because their first marriage is still valid in the eyes of the church and therefore they are seen to be living in an adulterous state of sin.
In the document the Pope sided with progressives who had proposed an "internal forum" in which a priest or bishop decide jointly with the individual on a case-by-case basis if he or she can be fully re-integrated and receive communion.
But Cardinal Mueller has said there should be no exceptions, making him a hero to conservatives who have made the issue a rallying point for their opposition to Pope Francis.