Pope Benedict XVI has announced he will resign from his post at the end of February following an eight-year reign dogged by sex scandals.
The 85-year-old pope, born Joseph Aloisius Ratzinger, has led the Catholic Church through some of the worst child sex abuse scandals in its history.
In 2005, Pope Benedict was personally accused of being involved in a cover-up of child sex abuse. He was said to have "obstructed justice" after it was found he issued an order to carry out investigations into child sex abuse in secret.
He made the order in a confidential letter sent to every Catholic bishop in May 2001.
At this time, the pope led the Congregation for the Doctrine of Faith, which is responsible for moral leadership, including responding to child abuse allegations.
In the letter, the pope said the bishops had the right to hold inquiries in secret and keep the evidence confidential for up to 10 years.
The letter was referred to in documents relating to a case where two children were sexually abused by a priest in Texas. Lawyers said the pope conspired to obstruct justice by keeping investigations secret.
In another case, Pope Benedict was accused of failing to act on allegations of sex abuse by ignoring letters sent to him by an archbishop in 1996.
In the letters, the archbishop called for disciplinary proceedings against the priest Lawrence Murphy, who was believed to have molested 2,000 deaf boys in Wisconsin between 1950 and 1974.
Victims said Murphy assaulted them during confession, in his office, in his car, at his mother's house and in their dormitory beds. He died in 1988.
The Vatican newspaper L'Osservatore Romano said there was no cover-up and that the incident was a smear attempt against the Pope.
A Vatican spokesman said there the case had only reached them years after Murphy had died and did not have a procedure for punishment.
Crimes against humanity
In 2011, victims of sex abuse by Catholic priests called for Pope Benedict to be tried for crimes against humanity at the international criminal court.
The Centre for Constitutional Rights and the Survivors Network of those Abused by Priests filed a complaint against Pope Benedict and three Vatican officials, saying they tolerated and enabled sex crimes.
Publicly, Pope Benedict has always condemned child sex abuse committed by Catholic priests and apologised to victims of abuse in Ireland in 2010.
In a letter, he said: "You have suffered grievously and I am truly sorry. Your trust has been betrayed and your dignity has been violated ... I openly express the shame and remorse that we all feel."
He said priests guilty of abuse will "answer before God and properly constituted tribunals for the sinful and criminal actions they have committed".
Victims said his statement fell short of their demands, which called for the church to admit it systematically covered up sex abuse.
More recently, Pope Benedict said abuse within the church was a "mystery", saying he could not understand why church officials committed sex crimes against vulnerable children.
Speaking to Irish Catholics in June last year, he said: "Thankfulness and joy at such a great history of faith and love have recently been shaken in an appalling way by the revelation of sins committed by priests and consecrated persons against people entrusted to their care.
"Instead of showing them the path towards Christ, towards God, instead of bearing witness to his goodness, they abused people and undermined the credibility of the Church's message.
"How are we to explain the fact that people who regularly received the Lord's body and confessed their sins in the sacrament of Penance have offended in this way? It remains a mystery.
"Yet evidently, their Christianity was no longer nourished by joyful encounter with Jesus Christ: it had become merely a matter of habit."