In common parlance, a devil's advocate is someone who takes a position, sometimes one he or she disagrees with, for the sake of argument. This process can be used to test the quality of the original argument and identify weaknesses in its structure.
During the canonization process of the Roman Catholic Church, the Promoter of the Faith (Latin Promotor Fidei), popularly known as the Devil's Advocate (Latin advocatus diaboli), was a canon lawyer appointed by the Church to argue against the canonization of the candidate. It was his job to take a skeptical view of the candidate's character, to look for holes in the evidence, to argue that any miracles attributed to the candidate were fraudulent, etc. The Devil's advocate was opposed by God's advocate, whose job was to make the argument in favor of canonization.
The office was established in 1587 during the reign of Pope Sixtus V and was abolished by Pope John Paul II in 1983. This abolition streamlined the canonization process considerably, helping John Paul II to usher in an unprecedented number of elevations: nearly 500 individuals were canonized and over 1,300 were beatified during his tenure as Pope as compared to only 98 canonizations by all his 20th-century predecessors.
Such a dramatic increase suggests that the office of the Devil's Advocate had served to reduce the number of canonizations by complicating the process. Some argue that it served a useful role in ensuring that canonizations did not proceed without due care and hence the status of sainthood was not easily achieved. In cases of controversy the Vatican may still seek to informally solicit the testimony of critics of a candidate for canonization. The British born American columnist Christopher Hitchens was famously asked to testify against the beatification of Mother Teresa in 2002, a role he would later humorously describe as being akin to "representing the Evil One, as it were, pro bono".
The novel The Devil's Advocate by Morris West depicts an English cleric sent from the Vatican to a faraway Italian village, to investigate the antecedents of a man believed by the villagers to have been a saint. In one passage the protagonist explains his reason for taking up the role of the Devil's advocate: "We have too many saints, and not enough sanctity."
Various other books, films and plays have the title "The Devil's Advocate," used in more loose and metaphorical contexts (see Devil's advocate (disambiguation)).
The Advocatus Diaboli is sometimes referred to as a team role. While some sources regard the role as a "destructive" team role, others see the role as a constructive one. According to the second group, The Advocatus Diaboli' task is improving decision making processes and preventing individuals and teams from decisions without sufficient consideration.